NVS TGT Science held on 28th Nov 2022 shift 1 (Previous Year Paper)

The correct answer is USA

Key Points

• Exercise Yudh Abhyas, conducted annually between India and USA with the aim of exchanging best practices, tactics, techniques and procedures between the Armies of the two nations.
• Indian and US militaries to conduct the battalion-level “Yudh Abhyas” exercise between 15th November 2022 to 2nd December 2022.
• The Yudh Abhyas will be held at Auli in Uttarakhand which from just 100 km from the Line of Actual Control (LAC).
• In August, the US and Indian forces conducted the “Vajra Prahar” exercise at Bakloh in Himachal Pradesh.

Additional Information

The correct answer is B and C only.

Key Points

• The constitution of India says that the Vice-President should not be a member of either the House of Parliament or a House of the state legislature.
• Vice President shall be elected by an Electoral college through a system of Proportional Representation by means of a Single Transferable Vote and the voting should be by secret ballot.
• He should not hold any other office of profit.

Additional Information

Vice President(VP)

• VP is the Ex-officio Chairman of the Council of States and shall not hold any other office of profit.
• The Vice President shall act as President in case of any occurrence of vacancy due to death, resignation or removal.
• Vice President can also act as President when the President is unable to discharge his function due to absence or illness.
• In such a period Vice President will be entitled with all the immunities, powers and privileges of the President.

Election

• Vice President shall be elected by an Electoral college through a system of Proportional Representation by means of a Single Transferable Vote and the voting should be by secret ballot.
• The electoral college consists of members of both houses of the Parliament.
• The Vice President shall not be a member of any house of the Parliament.

Qualification

• He must be a citizen of India.
• Completed the age of 35 years.
• qualified for election as a member of the Council of States.
• must not hold the office of profit.

Term

• Vice President can hold the office for a term of 5 years.
• He can resign addressed to President.
• He can be removed from his office by a resolution of the Council of states passed by the Majority of all the members of the Council and agreed to by the House of the People for which 14 day's notice period is required.
• Vice President continue to hold his office until his successor comes.
• The election for Vice President must be conducted before the expiration of the Term.
• In case of death, resignation or removal it should be conducted as soon as possible.

The correct answer is 26th November, 2022.

Key Points

• Every year, National Milk Day is celebrated on November 26 across India.
• The largest milk-producing country celebrates this day to demonstrate the importance of milk in everyone's life.
• It is celebrated to commemorate the birthday of the father of India’s White Revolution, Dr. Verghese Kurien (also nicknamed Milkman of India).

Additional Information

• World Milk Day is observed on 1 June every year by the United Nations.
• The theme of World Milk Day is Drink Milk: Today & Everyday.
• The first National Milk Day was celebrated on 26 November 2014 where various milk producers from 22 states participated.

The correct answer is National Research Foundation

Key Points

​ National Research Foundation

• The NRF is an independent statutory body established through the National Research Foundation Act (Act No 23 of 1998), following a system-wide review conducted for the Department of Arts, Culture, Science and Technology (DACST).
• The new entity incorporated the functions of the research funding agencies that were previously servicing various sections of the research community, namely the former Centre for Science Development (CSD) of the Human Sciences Research Council (HSRC) and the former Foundation for Research Development (FRD) that included several National Research Facilities.

Indian Council of Agricultural Research

• The Indian Council of Agricultural Research (ICAR) is an autonomous organisation under the Department of Agricultural Research and Education (DARE), Ministry of Agriculture and Farmers Welfare , Government of India.
• Formerly known as Imperial Council of Agricultural Research, it was established on 16 July 1929 as a registered society under the Societies Registration Act, 1860 in pursuance of the report of the Royal Commission on Agriculture.
• The ICAR has its headquarters at New Delhi.
• The Council is the apex body for co-ordinating, guiding and managing research and education in agriculture including horticulture, fisheries and animal sciences in the entire country.
• With 111 ICAR institutes and 71 agricultural universities spread across the country this is one of the largest national agricultural systems in the world.

The correct answer is Nikhat Zareen.

Key Points

• India's Nikhat Zareen has won the gold medal in the 52kg category at the Women's World Boxing Championships.
• She defeated Thailand's Jitpong Jutamas in the fly-weight final in Istanbul, Turkey on May 19.
• With this win, Nikhat becomes only the fifth Indian women's boxer after Mary Kom, Sarita Devi, Jenny RL and Lekha KC to win a gold at the World Championships.

Additional Information

• ​Women's World Boxing Championships is organised by the International Boxing Association.
• The International Boxing Association is an independent sport organization.
• It sanctions amateur boxing matches and awards world and subordinate championships.
• The International Boxing Association:
• Headquarters: Lausanne, Switzerland
• President: Umar Kremlyov
• Founded: 1946

The correct answer is Ministry of Education.

Key Points

• Ministry of Education  took the initiative of Atal Ranking of Institutions on Innovation Achievements (ARIIA).
• Atal Ranking of Institutions on Innovation Achievements (ARIIA) is an initiative of Ministry of Education (MoE), Govt. of India to systematically rank all major higher educational institutions and universities in India on indicators related to “Innovation and Entrepreneurship Development” amongst students and faculties.
• Major Indicators for consideration
• Budget & Funding Support.
• Infrastructure & Facilities.
• Awareness, Promotions & support for Idea Generation & Innovation.
• Promotion & Support for Entrepreneurship Development.
• Innovative Learning Methods & Courses.
• Intellectual Property Generation, Technology Transfer & Commercialization.
• Innovation in Governance of the Institution.

The correct answer is USA.

Key Points

• USA  was the world's largest exporter of major arms in 2017-21, as per 'Trends in International Arms Transfers, 2021' the latest fact sheet of the Stockholm International Peace Research Institute.
• The volume of international transfers of major arms in 2017–21 was 4.6  per  cent lower than in 2012–16, but was 3.9  per  cent higher than in 2007–11.
• The five largest arms exporters in 2017–21 were the United States, Russia, France, China and Germany.
• The five largest arms importers were India, Saudi Arabia, Egypt, Australia and China.
• Between 2012–16 and 2017–21 there were increases in arms transfers to Europe (19 per cent) and to the Middle East (2.8 per cent), while there were decreases in the transfers to the Americas (–36 per cent), Africa (–34 per cent), and Asia and Oceania (–4.7 per cent).

Additional Information SIPRI

• SIPRI provides data, analysis and recommendations for armed conflict, military expenditure and arms trade as well as disarmament and arms control.
• Following are the important details about SIPRI.              1. SIPRI Headquarters: Oslo, Norway.
               2. SIPRI Founded: 6 May 1966.
               3. SIPRI​ Director: Dan Smith.

The correct answer is To prohibit carbon emission.

 In News

• The aim of the Energy Conservation (Amendment) Bill, 2022  is to prohibit carbon emission.
• It provides for the regulation of energy consumption by equipment, appliances, buildings, and industries.
• The Electricity conservation act, 2001 which was last amended in 2010 is now being reformed in order to introduce changes inculcating clean energy as a major source of energy production.

Highlights of the Bills

• Obligation to use non-fossil sources of energy: Bill states that the government may require the consumers to meet a minimum share of energy consumption from non-fossil sources.
• Carbon trading: Bill empowers the central government to specify a carbon credit trading scheme.
• Energy conservation code for buildings: Bill provides for an ‘energy conservation and sustainable building code’ for green buildings.
• Applicability to residential buildings: Bill provides the new energy conservation and sustainable building code which will apply to the office and residential buildings.
• Under earlier Act, the energy conservation code applies to commercial buildings with certain criteria.
• Standards for vehicles and vessels: Bill expands the scope to include vehicles (as defined under the Motor Vehicles Act, 1988) and vessels including ships and boats.
• Increase members in Governing Council of Bureau of Energy Efficiency.

Additional Information Significance of the bill

• The bill facilitates in achieving Panchamrit principles initiated by India in COP-26 at the Glasgow summit, 2021.
• It will help in promoting renewable energy and development of domestic Carbon market to fight climate change.
• The changes will succor in reducing about 550 tonnes of carbon dioxide equivalent by 2030.
• It will pave way for introduction of new concepts such as Carbon trading and will help in adopting clean technologies.

Provisions in the Energy conservation act, 2001

• The act led to the establishment of Bureau of Energy efficiency(BEE) which can specify qualifications required for energy auditors.
• It empowers the Centre to specify norms and standards of energy efficiency for appliances, industrial equipment and buildings.
• Consumers who consume excess energy can be penalized for the excess consumption.
• The act allows centre to issue energy certificates to industries that consume less than their maximum allotted energy.

The correct answer is Rafael Nadal.

Key Points

• Spaniard Rafael Nadal on 5 June 2022 won the 14th singles title of the French open beating Casper Ruud of Norway 6-3, 6-3, 6-0 in the final.
• With this victory, 36-year-old Nadal has become the oldest champion of the French Open.
• It is his 22nd Grand Slam title.
• In women's singles, World Number One Iga Swiatek of Poland won the 2022 title by beating Coco Gauf in Paris on 4 June 2022.
• | Grand Slam Title 2022 | Male Winner | Female Winner | | --- | --- | --- | | U.S. Open | Carlos Alcaraz | Iga Swiatek | | Wimbledon | Novak Djokovic | Elena Rybakina | | French Open | Rafael Nadal | Iga Swiatek | | Australian Open | Rafael Nadal | Ashleigh Barty
  |

Additional Informations

• The French Open, also known as Roland-Garros, is a major tennis tournament.
• It is held over two weeks at the Stade Roland Garros in Paris, France, beginning in late May each year.
• The tournament and venue are named after the French aviator Roland Garros.
• ​The French Open:
• Founded: 1891
• Location: Paris, France
• Surface: Clay – outdoors (1908–present); Sand – outdoors (1891–1907)
• Japan's Ena Shibahara and Wesley Koolhof of the Netherlands won the French Open mixed doubles title on 2 June 2022.

The correct answer is Frank Wilczek.

Key Points

• Dr. Frank Wilczek, a Nobel Prize-winner theoretical physicist and author, receives the 2022 Templeton Prize.
• The Templeton Prize, valued at more than $1.3 million, is one of the world’s largest annual individual awards.
• Established by the late global investor and philanthropist Sir John Templeton, it is given to honor those who harness the power of the sciences.

Additional Information

• The Templeton Prize was established in 1972 by John Marks Templeton, an American-born financial entrepreneur who sought to advance human knowledge of the universe through a broad set of intellectual approaches and an ecumenical perspective on spiritual progress.
• Though the prize is considered by some to be the equivalent of a Nobel Prize for religion, recipients may be of any profession, and emphasis is often placed on work that explores the intersections between spirituality and science.

The logic followed here is: 

Assertion (A) : Plaster of Paris is used for setting fractured bones by doctors.

→ True, Plaster of Paris is mixed with water and used around the fractured limb, it sets into a hard mass and keeps the bone joints in a fixed position, and is used for setting fractured bones.

Reason (R) : If Plaster of Paris is mixed with water and used around the fractured limb, it sets into a hard mass.

→  The Reason is the correct explanation of A, as Plaster of Paris is used for setting fractured bones.

Hence, the correct answer is "Both A and R are true and R is the correct explanation of A".

Given statement: 

Q < W, 

D < Q, 

W = L

On Combining: D < Q < W = L

Conclusions :

i) D < W →  FALSE (as D < Q < W = L gives; D < W → so it is definitely false).

ii) L ≥ Q →  FALSE (as D < Q < W = L gives; Q < L →so it is definitely false).

Hence, the correct answer is "Neither conclusion I nor II is true".

Given: 24, 96, 48, 192, ? , 384, 192

The logic follows here is:

Hence, the correct answer is "96".

The logic follows here is:

Each letter is increased by +5.

Thus, the next term of the given series is 'N'.

Hence, the correct answer is "N".

Statement:

Indians prefer to wear cotton clothes in summer.

Conclusions:

I. Cotton clothes are more comfortable during summer.

→ True, because cotton is a highly absorbent fabric and can easily absorb sweat from the skin during summer. Thus, cotton clothes are more comfortable during summer.

Thus, conclusion I follows.

II. India is a hot country.

→ False, because we cannot conclude that India is a hot country only because Indians prefer to wear cotton clothes in summer.

Thus, conclusion II does not follows.

Hence, the correct answer is "Only conclusion I follows".

According to the given information:

If North-West becomes South, South-West becomes East and so on, then the new arrangement is:

Thus, South-East becomes 'North'.

Hence, the correct answer is "North".

Asper the given information:

The Venn Diagram that best represents the relationship among three groups of people - Fathers, Sons, and Men is as follows:

• Fathers and Sons both are Men
• Some Fathers are son and some sons are also fathers.

Hence, the correct answer is "option 4".

As per the question,

• A is the brother of B; C is the mother of A; and F is the son of A.

• B is the granddaughter of D

​

Thus, F is 'Great Grandson' of D.

Hence, the correct answer is "Great Grandson".

As per the question,

Four friends A, B, C and D compared their height.

A is taller than B but shorter than C.

• C > A > B   ---------------(1)

D is shorter than C but taller than A.

• C > D > A   ---------------(2)

​Thus, the final arrangement after combining both (1) and (2) is:

• C > D > A > B

​Clearly, 'C is the tallest' is true.

Hence, the correct answer is "C is the tallest".

The logic follows here is:

I. 'Ya Na Sa' means 'I am good' and 'Sa Na Ke' means 'I am hungry'.

Here, the code for 'good' is Ya.

So, I alone is sufficient to answer.

II. 'Pi Ya Se' means 'She is good' and 'Ya Su To' means 'You are good'.

Here, the code for 'good' is Ya.

So, II alone is also sufficient to answer.

Therefore, either of the statements is sufficient to find the code for 'good'.

Hence, the correct answer is "Either I or II is sufficient".

​Input devices are electromagnetic devices that receive information or a set of instructions from the outside world. 

Key Points

• It converts that information into a format that is accessible and intelligible by machines.
• Computer input devices act as an interface for the computer's proper communication with the outside environment.
• Users can save the data they enter via a variety of input devices in the computer's memory for later processing and preparation.
• A computer can be communicated with and controlled using an input device, which transmits data to the computer.
• The most common input devices are Keyboard, Mouse, Joy Stick, Light Pen, Microphone, Scanner, and Barcode Reader.

Thus, a Plotter is a device that can not be used as an input device in a computer system. 

Additional Information

• A plotter is an output device that produces vector graphics drawings.

Password security is a set of regulations, procedures, and technological advancements that increase the security of passwords and authentication procedures. 

Key Points

• The first line of security against unwanted access to computers and personal information is provided by passwords.
• The computer will be more secure from hackers and bad malware.
• The effective practice to secure our passwords are: 
• Never reveal passwords to others.
• Use multi-factor authentication (MFA)
• Use password managers
• Length trumps complexity
• Change it frequently
• Don't write down any in a file.

Thus, Passwords should contain memorable data for the easy recall is not an effective practice to secure our passwords.

A firewall creates a wall between a trustworthy network and an unreliable network. 

Key Points

• A firewall is a network security device used in computing that monitors and regulates incoming and outgoing network traffic.
• A firewall is essentially the barrier that stands between a private internal network and the open Internet at its most basic level.
• Firewalls can stop harmful software from connecting to a computer or network over the internet.
• It sets security policies that are used to monitor and filter incoming and outgoing network traffic through a firewall.

Thus,  I am Firewall. 

Additional Information

• Cookies are short data packets created by a web server while a user is accessing a website.
• Malware is a programme or file that purposefully hurts a computer, network, or server.
• Antivirus software is a computer programme intended to stop, find, and get rid of the malware.

Microsoft produced Microsoft Excel is a spreadsheet for Windows, macOS, Android, and iOS. 

Key Points

• The fundamental capabilities of all spreadsheets are present in Microsoft Excel.
• It organises data manipulations like arithmetic operations using a grid of cells arranged in numbered rows and letter-named columns.
• It has a variety of built-in functionalities to address financial, engineering, and statistical requirements.
• It has a very limited three-dimensional graphical display and can present data as line graphs, histograms, and charts.

Therefore, MS Excel software of the Microsoft Office package is the best suited for this purpose. 

Additional Information

• MS PowerPoint is created to provide graphics for group presentations.
• Microsoft Access is a database management system (DBMS) that combines a graphical user interface.
• MS Word is a word processor that may be used to create papers, letters, reports, and other types of writing.

Unix is not an example of a web browser.

Key PointsBrowser:

• A web browser is a software application for accessing the information on the World Wide Web.
• When a user requests a web page from a particular website, the web browser retrieves the necessary content from a web server and then displays the page on the user's device.
• It is an application used to access and view websites.
• Microsoft Internet Explorer, Maxthon 6 Cloud Browser, Google Chrome, Opera, Mozilla Firefox, Apple Safari, etc. are some of examples of web browser
• A web browser is a computer program you use to view web pages
• A web browser helps in receiving the web-page matter through the internet.

Important PointsUnix operating system:

• The Unix operating system is generally known as Multi-user operating system
• UNIX is a multitasking, multi-user operating system that exists in many variants.

The Internet is a system of worldwide connected computer networks that communicate with one another using the Internet protocol suite. 

Key Points

• It is made up of a vast array of electrical, wireless, and optical networking technologies.
• ​Internet each of its constituent networks establishes its own rules for access and usage.
• Services available on the Internet include: 
• Locating people using social networking sites
• Downloading and uploading files from or to remote sites
• Playing community games
• Maintaining journals
• Forming groups and sharing views with like-minded people

Therefore, Statements a, b, c, d, e are correct.

Antivirus software is a programme or set of programmes. 

Key Points

• It is designed to look for, identify, stop, and get rid of computer viruses that can harm the system.
• Antivirus software may also find and get rid of other unwanted programmes like worms, adware, and other threats.
• Antivirus software operates by comparing the files and programmes on your computer to a database of known malware types.
• It will also check systems for the presence of fresh or undiscovered malware threats
• The antivirus searches its database for matches by comparing files, programmes, and applications entering and leaving the computer.

Therefore, I am Antivirus. 

Additional Information

• A firewall is a network security device used in computing that monitors and regulates incoming and outgoing network traffic.
• Cookies are short data packets created by a web server while a user is accessing a website.
• Malware is a programme or file that purposefully hurts a computer, network, or server.

CU or Control Unit is a part of the Central Processing Unit.

Key Points

Control Unit in ALU:

• A control unit (CU) is an integrated circuit in a processor that controls the input and output.
• It receives instructions from a program, then passes them to the Arithmetic Logic Unit (ALU).
• ​This unit enables the sequential flow of data between the different parts of the Central Processing Unit.
• It can interpret instructions and perform the necessary actions.

Spam is not an abbreviation for a computer threat. 

Key Points

• Spam is unwanted, uninvited digital communication transmitted in bulk.
• Spam is frequently transmitted by email, but it can also be sent through social media, text messages, and phone calls.
• Spammers transmit their unwanted messages in mass through a variety of communication channels.
• There are different types of Spam such as Phishing emails, Email spoofing, Tech support scams, Current event scams, Advance-fee scams, and Malspam.

Therefore, I am Spam. 

Additional Information

• A virus is a form of malware that accompanies another programme and has the ability to multiply and propagate once it has been run on a machine.
• Hacker is an expert who employs non-standard methods to accomplish a goal or get around a challenge within a computerised system.
• Spyware is malicious software such as spyware placed on a computer without the end user's knowledge.

The correct answer is Ctrl + Z.

Key Points 

• To undo an action press Ctrl+Z.
• If you prefer your mouse, click Undo on the Quick Access Toolbar.
• You can press Undo (or CTRL+Z) repeatedly if you want to undo multiple steps.
• Undo means to destroy the effect of something that has already happened.

Additional Information 

Important Shortcut keys used in MS Word:

• Cut the selected content to the Clipboard - Ctrl+X
• Copy the selected content to the Clipboard - Ctrl+C
• Paste the contents of the Clipboard -Ctrl+V
• Increase the font size by 1 point.- Ctrl+]
• Center the text - Ctrl+E
• Align the text to the left - Ctrl+L

Teachers are individuals who have elaborate systems of knowledge for understanding problems in teaching and learning. They have the necessary awareness of the theoretical and practical aspects related to teaching and learning. 

Key Points Teachers not only plan and teach but also evaluate the performance of the learners and take up necessary remedial measures to help them improve their learning.

• For good teaching in the class, first of all, a teacher should be well aware of the response that he is looking for in the class.
• Sensing that learners are bored, a teacher decides to stop teaching.
• Realizing that a learner has not understood a point fully, a teacher decides to simplify the explanation with more examples.
• In order to make a lesson more interesting, a teacher decides to narrate a related story.
• As learners start making too much noise and can not be managed by a teacher, she decides to let them go out and play.
• As the prepared plan does not prove effective to make learners understand the point, a teacher decides to deviate from the plan and tries out another sequencing of learning experiences.
• Recognizing a learner’s attention behavior, managing deviant behavior, recognizing learner needs, etc. that occur along with teaching are all part of the management process while teaching.

Thus, it is concluded that for good teaching in the class, first of all, a teacher should be well aware of the response that he is looking for in the class.

Interaction (or interactivity) between the teacher and student is an important aspect of the teaching-learning process. Teaching-learning should not be a one-sided activity of presenting information to the students.

Key Points

• Effective interaction in the classroom should ideally generate a flow of ideas.
• By actively participating in discussions and exchanging ideas, students learn to analyze information, question assumptions, and come up with creative solutions.
• Discussing different viewpoints and perspectives on a topic helps students develop a deeper understanding of the material and consider multiple angles.
• A classroom that encourages open sharing of ideas fosters a safe and supportive environment for students to explore their creativity and generate innovative solutions.

Hence, we can conclude that effective interaction in the classroom should generate a flow of ideas.

Frustration results from the blocking of needs and motives by something or someone that hinders us from achieving the desired goal. There could be a number of causes of frustration such as social discrimination, interpersonal hurt, low grades in school, etc. 

Key Points The term frustration refers to the blocking of behavior directed towards a goal. If motives are frustrated or blocked, emotional feelings and behavior often result.

• People who cannot achieve their important goals, feel depressed, fearful, anxious, guilty, or angry.
• Often they are simply unable to drive ordinary pleasure for living.
• Frustration creates uncomfortable emotional tensions that operate as insistent drives influencing the individual to change in various tension-reducing activities.
• The frustration of one's motive always results in downgrading self-concept.
• Self-concept is the self-knowledge we have about ourselves in various aspects such as physical characteristics, social roles, personality traits, interests, skills, etc.
• Self-concept is multi-dimensional.

Thus, it is concluded that the frustration of one's motive always results in downgrading self-concept.

Human growth and development is an orderly, predictable process beginning with conception and continuing until death. It involves many complex changes in all dimensions of a person through the life span.

Key Points Sunita, aged 5, tends to repeat a particular 'act' over and over; then moves on to another 'act', which in turn she repeats again. Her behavior indicates nothing unusual, this is a normal process of development.

• Each person progresses through definite phases of growth and development, but the pace and progression of this development are highly individual.
• Development refers to a progressive increase in skill and capacity to function which causes the qualitative change from a lower to a more advanced stage of complexity.
• Development is orderly and reasonably enduring.
• The development also refers to intellectual, moral, emotional, sexual, social, language, speech, and spiritual developments.
• It is a set of skills and competencies peculiar to each stage of development that must be accomplished by the children to deal effectively with their environment.

Thus, it is concluded that Sunita, aged 5, tends to repeat a particular 'act' over and over; then moves on to another 'act', which in turn she repeats again. Her behavior indicates nothing unusual, this is a normal process of development.

Critical thinking aims at simplification/ generalization on the one hand and truth and accuracy on the other. It scrupulously adheres to establish canons of logic. 

Key Points Teaching is the process of facilitating learning by leading discussions, asking open-ended questions, and acquiring knowledge by active participation. For developing creative thinking among the students,  Open-ended and subjective questions type of questions should be asked the teacher.

• Open-end questions consist of questions that require short or lengthy answers by the respondents.
• An open-ended question permits the respondents to answer in their own words.
• Open-ended questions give liberty to the respondents to express their views.
• It gives tremendous freedom to the respondents to answer according to their interpretation.
• Unanticipated answers can be obtained from the respondents.
• The researcher can get the real views of the respondents.
• The respondent needs more time to answer.
• Respondents may use different terms for the same concept.

Thus, it is concluded that for developing creative thinking among the students,  Open-ended and subjective questions type of questions should be asked the teacher.

Additional Information

Any visual aid which is used for the magnification of an image on a screen in dark or semi-dark conditions can be called a projected visual aid. 

Key Points Projected aids are “projected” onto a wall or screen using machines. On projection, the message on a slide or transparency gets magnified several times and hence can be seen by a large group of students.

Examples of Projected Aids are Overhead Projectors,  Epidiascope, Slide projectors, Films, video, Compact discs or CDs, and Computer and PowerPoint Presentations.

Thus, it is concluded that the Blackboard is not a projected teaching aid.      

Additional Information 

The term teaching refers to the actions of someone who is trying to assist others to reach their fullest potential in all aspects of development.

Key PointsThe nature and objectives of teaching are:

• (a) Teaching and learning are integrally related. - Correct. Teaching and learning are two sides of the same coin. They are connected processes. Effective teaching leads to effective learning.​
• (c) Concern of all teaching is to ensure social transformation in students. - Correct. While not the only objective, teaching does play a significant role in facilitating social transformation by imparting knowledge, fostering critical thinking, and promoting social values.
• (f) Teaching is a social act whereas learning is a personal act. - Correct. Teaching is a social act as it often involves interaction, communication, and collaboration, while learning, although it can occur in social contexts, is ultimately a personal act as it is up to the individual to absorb and process the information.

Hint

• (b) There is no difference between teaching and training. - Incorrect. Teaching often refers to acquiring knowledge and understanding, while training is about acquiring a specific skill.
• (d) All good teaching is formal in nature. - Incorrect. Good teaching can happen in both formal (schools, colleges) and informal (home, social interactions) settings.
• (e) A teacher is a senior person. - Incorrect. A teacher can be of any age and experience often comes with age.

Thus, it is concluded that (a), (c) and (f) are correct

Evaluation is the systematic process of determining the extent to which the specified instructional objectives previously identified and defined have been achieved. The process of evaluation is based on the relationship between the objectives of the content and its actual outcome. 

Key Points Evaluation is both qualitative and quantitative, it may be 'formative' (during the process of development) or 'summative' (at the end of the total program or each phase thereof).

 During curriculum development, the evaluation used to improve content learning is called formative evaluation.

• Formative evaluation is used to monitor the learning progress of students during the period of instruction.
• Its main objective is to provide continuous feedback to both teacher and student concerning learning successes and failures while instruction is in process.
• Feedback to students provides reinforcement of successful learning and identifies the specific learning errors that need correction.
• Feedback to teachers provides information for modifying instruction and for prescribing group and individual remedial work.
• The formative evaluation depends on tests, quizzes, homework, classwork, and oral questions prepared for each segment of instruction.

Thus, it is concluded that during curriculum development, the evaluation used to improve content learning is called formative evaluation.

Additional Information 

The term teaching refers to the actions of someone who is trying to assist others to reach their fullest potential in all aspects of development. Teaching results when the teacher does any activity with the intention that his/her learners would learn something as a result of it.

Key Points

 The nature of the "teaching" profession are:

• The teacher should not only facilitate learning but should promote citizenship training and active integration with society, developing curiosity, critical thinking, creativity, initiative, and self-determination.
• The profession of teaching is learner-oriented, dynamic, and humane.
• The teacher should help in coordinating and enriching the efforts of students and other resources engaged in the task of teaching-learning.
• To acquire knowledge and understanding of instructional planning, preparation, transaction, and evaluation.
• To apply knowledge and understanding to new and unfamiliar teaching situations.
• To develop proper interests, attitudes, and values relating to the teaching profession and procedures.
• To develop the abilities for effective classroom management.

Thus, it is concluded that helping in being obedient to the Government is not the nature of the "teaching" profession.

In classrooms, learning often proceeds most effectively when there is rapid feedback provided by the teacher.

Key Points

• Feedback allows students to understand how well they are grasping the material, identify areas for improvement, and make necessary adjustments to their learning strategies.
• This reinforces learning and helps them understand concepts more deeply.
• Timely feedback helps students gauge their progress and identify areas for improvement. It keeps them engaged and motivated in the learning process.
• Addressing errors and providing clarification early on prevents misconceptions and fosters a better understanding of the material.

Hence, we can conclude that in classrooms, learning proceeds most effectively if there is rapid feedback from the teacher.

Explanation:

• Acceleration is the rate of change of velocity per unit of time.
• $a = \frac{dv}{dt}$
• Where, dv = change in velocity, dt = change in time

Uniform acceleration

• If the velocity of object changes by equal amounts in equal intervals of time, then it is called uniform acceleration or constant acceleration
• The graph of uniform acceleration is a straight line with a positive slope.

• Acceleration increases the velocity per second

Non-uniform acceleration -

• If the velocity of object changes by unequal amounts in equal intervals of time, then it is called non-uniform acceleration.
• The graph for non-uniform acceleration is not a straight line.

​

Retardation

• It is just the reverse of acceleration and is defined as a decrease in velocity per unit of time.
• $a' = - \frac{dv}{dt}$

Uniform Retardation -

• If the velocity of an object decreases by equal amounts in equal intervals of time, then it is called uniform retardation or constant retardation
• The graph of uniform retardation is a straight line with a negative slope

• Retardation decreases the velocity per second
• Non-uniform retardation - if the velocity of an object decreases by unequal amounts in equal intervals of time, then it is called non-uniform retardation.
• The graph for non-uniform acceleration is not a straight line.

 

Additional Information

• Instantaneous acceleration is the acceleration of the object at a specific instant during the motion.

Concept:

Average speed:

• It is defined as the distance per unit of time.
• Formula, $Average , , speed=\frac{Distance}{Time}$
• The SI unit of average speed is m/s.

Calculation:

Given,

The radius of the circle, r = 20m

Time, t = 10s

The average speed of the particle is defined as the distance per unit of time.

$v_{a}=\frac{\pi r}{t}$

$v_{a}=\frac{ \pi \times 20}{10}=2\pi ~m/s$

Hence, the average speed of the particle is $2\pi ~m/s$

Concept:

Distance:

• The complete length of the path between any two points.
• It is a scalar quantity because it has only magnitude.
• To calculate distance, the direction is not considered.

Displacement:

• The direct length between any two points when measured along the minimum path between them.
• It is a vector quantity because it has both magnitude and direction.
• To calculate displacement, the direction is taken into consideration.

Calculation:

Given,

The radius of the circle, r = 1m

The distance (Displacement) of AB can be calculated from the Pythagotous theorem,

AB² = AC² + CB²

$AB=\sqrt{1^2+1^2}= \sqrt{2} ~m$

$AB=\sqrt{2} ~m$

Distance = 3/4(2πr) = 1.5 πr

Distance = 1.5 π

Concept:

• Acceleration is the rate of change of velocity with respect to time
• $a = \frac {dv}{dt}$
• Where dv is the change in velocity and dt is the change in time.
• Acceleration is a vector quantity.
• When a body is falling freely then an acceleration is acting on it, which is the acceleration due to gravity.

In Circular Motion there are two types of acceleration

1. Tangential acceleration, which is responsible for the change in magnitude given by $a = \frac {dv}{dt}$
2. Centripetal acceleration, which is responsible for the change in the direction given by $a=\frac{v^2}r$

Explanation:

In statement A - An object released from a certain height, then

• its initial velocity is zero,
• Also, it is falling freely, then it has acceleration due to gravity.

​In statement B - A ball is thrown up, then

• Its velocity becomes Zero when it reaches to a maximum height
• Also, it is the case of the free-falling body, so it has acceleration due to gravity.

​​In statement C - An object moving in a uniform circular motion

• Now in a uniform circular motion, the magnitude of velocity is constant, but the direction varies, which means the angular velocity or speed is constant, hence the tangential acceleration is zero.
• But the centripetal acceleration is always present which is responsible for the circular path as it is always directed towards the center.

So, in cases, A and B, the velocity of an object may be zero at some instant, but its acceleration is not zero at that instant

Concept:

One-dimensional motion:

• Motion along a straight line or motion in one particular direction.
• Examples:
• ​Consider a car or a person driving down a straight road or jogging on a straight track.
• Think of an object being tossed vertically into the air and then watching it fall.

Two-dimensional motion:

• Two-dimensional (2D) motion means motion that takes place in two different directions (or coordinates) at the same time.
• The simplest motion would be an object moving linearly in one dimension.
• An example of linear movement would be a car moving along a straight road or a ball thrown straight up from the ground.

Explanation:

• In (1), at the same time particle has two positions which are not possible.
• 
• In (2), the particle again has two positions at the same time.
• 
• In (3), this graph represents the one-dimensional motion of a particle.
• 
• In (4), speed is negative which is not possible for motion in one dimension.
• 

Concept:

Newton's universal law of gravitation: 

• The force of attraction between any two bodies is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them.
• Formula, Force, $F =G\frac{m_1m_2}{r^2}$,
• Where, m₁, m₂ are the masses of the body, r = distance between the two bodies, G = universal gravitational constant
• The SI unit of the force is Newton (N).
• The gravitational forces do not depend on the medium.

Explanation:

The gravitational force does not depend on the medium, so the gravitational force is the same when it is placed in a liquid medium of relative density 4.

Hence, the correct option is 3,

Concept:

Force:

• It is defined as the product of mass and acceleration.
• Formula, F = ma, where m = mass, a = acceleration
• The SI unit of force is Newton.

Acceleration:

• It is defined as the rate of change of velocity.
• Formula, $a=\frac{dv}{dt}$
• The SI unit of acceleration is m/s².

Calculation:

The total mass, M = 3 + 2 + 1 = 6 kg

The total force applied, F = 18 N

Acceleration, $a =\frac{F}{m}$

$a =\frac{18}{6}=3~m/s^2$

The net force on the 2 kg is, F = 2 × 3 = 6 N

Concept:

Force:

• The force is defined as the product of mass and acceleration.
• The dimensional formula of the force is given as, [F] = [M L T^-2]
• 1 kg-wt = 9.8 N= 9.8 kg m/s²
• The force is directly proportional to the mass and acceleration.

Explanation:

Let the air resistance force acting on the balls be F.

• In the absence of air resistance, all objects fall at the same rate regardless of their mass. This is one of the fundamental principles of free fall and was famously demonstrated by Galileo.
• Therefore, assuming that air resistance acting on the balls is the same, both ball A and ball B will reach the ground at the same time, assuming no other forces are acting on them.

Concept:

• This quantity of energy transferred by the force to move an object is termed work done.
• The work done by gravity is equal to the change in potential energy.
• The potential energy is equal to the product of mass, and acceleration due to gravity and height.
• Formula, W = mgh, where m = mass, g = acceleration due to gravity, h = height

Calculation:

The work done by Rahul is, W = mgh

W = mgh 

W = 1 × 10 × 2

W = 20 J (upward, as the ball moves up)

Force applied by Rahul and displacement of the body in the same direction, Hence the workdone will be positive.

The work done by gravity is equal to the change in potential energy.

Gravity acts downward, opposite to the direction of motion, so the work done by gravity is negative.

Work done  = Force × displacement = mgh = 1 × 10 × 2 = - 20 J  (downward, as gravity opposes the motion)

 Note- 

1. The work done by gravity will be negative when moving away from the source of gravity. 

2.The work done by gravity will be positive when moving towards from the source of gravity.

Concept:

Force:

• It is defined as the product of mass and acceleration.
• Formula, F = ma, where m = mass, a = acceleration
• The SI unit of the force is Newton.

Equation of motion:

• The first equation of motion: v = u + at
• The second equation of motion: s = ut +0.5 at²
• Third equation of motion: 2as = v² - u²
• Here, v = final velocity, u = initial velocity, a  = acceleration, t = time

Calculation:

Given,

The mass of the ball, m = 50g

From the graph, 

The initial velocity, u = 3 m/s

The final velocity, v = 0m/s

Time, t = 10s

From the first equation of motion,

v = u + at

$a=\frac{v-u}{t}$

$a=\frac{0-3}{10}=-0.3 m/s^2$

The force exerted on the table, 

F = ma

F = 50 × 10^-3 × (-0.3) = - 0.015 N

Here, the negative sign indicates that the direction of force is opposite.

Concept:

Momentum:

• It is defined as the product of mass and velocity.
• Formula, P = mv, where m = mass, v = velocity
• Its SI unit is kg m/s.

Conservation of linear momentum:

• It states that if two objects collide, then the total momentum before and after the collision will be the same if there is no external force acting on the colliding objects.
• Formula, m₁u₁ + m₂u₂ = m₁v₁ + m₂ v₂

Calculation:

Given, 

The mass of the bullet, m = 25g

The velocity of the bullet, v = 120 m/s

The mass of the pistol, M = 2.5 kg

From the conservation of the momentum,

mv +  MV= 0

$V=-\frac{mv}{M}$

$V=-\frac{25\times 10^{-3}\times 120}{2.5}=-1.2 m/s$

Hence, the recoil velocity is -1.2 m/s.

Concept:

• Buoyant force or upthrust is the upward force exerted by a fluid that opposes the weight of an object immersed partially or fully in a fluid.
• Its magnitude of buoyant force is equal to the weight of fluid displaced.
• F_B = ρ'gV'
• Where, ρ'= density of the fluid, V' = volume submerged in the liquid, g = acceleration due to gravity.
• ​The buoyant force acts vertically upward, in opposition to the gravitational force that causes it.
• F_B = F_g = ρgV
• Where, ρ = density of the object, V = volume of the object, g = acceleration due to gravity.

​Calculation:

Let the density of object X is ρ_X and the object Y is ρ_Y

The density of water is ρ 

Given, for object X, volume submerged in water, $V' = \frac V2$

Then, $F_{BX} = ρgV' = ρg\frac V2$

This will balance the weight of body X

Then F_BX = F_g 

$\Rightarrow ρg\frac V2 = \rho _xgV$

$\Rightarrow \rho _x = \frac ρ2$ --- (1)

Now, for objects Y, volume submerged in water,$V' = V - \frac V4 = \frac {3V}4$

This will balance the weight of body Y

Then F_BY = F_g  

$\Rightarrow ρg\frac {3V}4 = \rho _ygV$

$\Rightarrow \rho _y = \frac {3ρ}4$ --- (2)

From equation 1 and 2 the ratio of density of X to that of Y is

$\frac{\rho _x}{\rho _y} = \frac 23$

Concept:

Concave mirror:

• ​A mirror has a reflective surface that is curved inward and away from the light source.

• Light converges at a point when it strikes and reflects back from the reflecting surface of the concave mirror. Hence, it is also known as a converging mirror.
• When the concave mirror is placed very close to the object, a magnified, erect, and virtual image is obtained.
• However, if we increase the distance between the object and the mirror then the size of the image reduces and a real and inverted image is formed.
• The image formed by the concave mirror can be small or large and can be real or virtual.

Explanation:

If a part of the mirror is covered with an opaque object then the intensity of the image formed will decrease as the image will be formed by less number of light rays.

Concept:

• lens is a transmissive optical device that focuses or disperse light beam using refraction.
• Two types of lenses: Concave lens and convex lens

Concave lens: 

• It is flat in the middle and thicker at the edge.
• It is also known as a diverging lens because it bends the parallel light rays outwards and diverges them at the focal point.

Convex lens: 

• It is thick in the middle and thinner on the edge.
• This lens is also known as a converging lens because it converges all light at a point called the focus.

. 

• The working principle of the lens is the law of refraction.
• The total power of the two lenses when placed in contact, P = P1 + P2
• The power of the lens is inversely proportional to its focal length, $P=\frac {1}{f}$

Lens formula, $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$ where v = image distance, u = image distance, f = focal length

Explanation:

Explanation:

Given, Power, P₁(L₁) = 10D , P₂ (L₂) = 12.5 D

The distance between the two lenses, d = 44 cm

For the first convex lens L₁, f = 1/P =100/10 = 10 cm

Given, u = - 20 cm, f = 10 cm

Lens formula, $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

$\frac{1}{10}=\frac{1}{v}-\frac{1}{-20}$

v = +20 cm

For the second convex lens L₂, f = 1/P =100/12.5 = 8 cm

Object distance, u = - 44 - (-20) = - 24 cm, focal length, f = 8 cm

Lens formula, $\frac{1}{8}=\frac{1}{v}-\frac{1}{-24}$

v = 12 cm

The distance between the original object and the final image is 

= 20 + 44 + 12 = 76 cm

Concept:

Refraction of light:

• It is the bending of light (it also happens with sound, water, and other waves) as it passes from one transparent substance into another.
• This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms, and rainbows.
• Even our eyes depend upon this bending of light.

• When light travels from a denser medium to a rarer medium, it bends away from the normal.
• When light travels from a rarer medium to a denser medium, it bends toward the normal,

Refractive index:

• It is the ratio between the speed of light in air to the speed in a medium.
• Formula, refractive index, $\mu =\frac{c}{v}$ where c = speed of light in air, v = speed of light in the medium

Explanation:

• A ray of light passes from a block of ice (n = 1.31) to kerosene (n = 1.44).
• In kerosene, it bends towards the normal and the speed of light in this medium is reduced.

Concept:

Refractive index:

• It is the ratio between the speed of light in air to the speed in a medium.
• Formula, refractive index, $μ =\frac{c}{v}$
• In terms of the wavelength, it is equal to the ratio of the wavelength of light in air to the wavelength of light in the medium.
• Formula, $μ =\frac{λ_0}{λ}$ where, λ₀ = wavelength in the air, λ = wavelength in the medium.

Calculation:

Given, 

The refractive index, μ = 1.5

The wavelength in the vacuum, λ₀ = 6000 Å

We  know that, $μ =\frac{λ_0}{λ}$

$\lambda =\frac{λ_0}{\mu}$

 $\lambda =\frac{6000}{1.5}$

λ = 4000 Å

Concept:

Kinetic energy:

• Kinetic energy is defined as the energy possessed by a body by a virtue of its motion.
• The formula of kinetic energy, $K=\frac{1}{2} mv^2$, where m= mass of the body, v= velocity of the body

Potential energy

• It is the energy possessed due to the position of the object is called potential energy
• The potential energy due to gravitation, P.E = mgh, where m = mass, g = acceleration due to gravity, h = height
• The second equation of motion under the influence of gravity,

           h = ut - 0.5 gt2

• From the first equation of motion under the influence of gravity, v = u - gt

Calculation:

Given,

The mass of the body, m = 200 g

The initial velocity of the body, u = 40 m/s

The time, t = 1.0 s

From the second equation of motion under the influence of gravity,

h = ut - 0.5 gt²

h = 40 × 1 - 0.5 × 10 × 1²

h = 35 m

From the first equation of motion under the influence of gravity,

v = u - gt

v = 40 - 10 × 1

v = 30 m/s

The ratio of the potential energy and kinetic energy is,

$\frac{P}{K}=\frac{mgh}{0.5 mv^2}=\frac{gh}{0.5v^2}$

$\frac{P}{K}=\frac{10\times 35}{0.5\times 30^2}$

$\frac{P}{K}=\frac{7}{9}$

Concept:

Heat transfer:

• Heat can travel from one place to another in several ways: Conduction, radiation, and convection.
• The resistance also depends on the temperature.
• In metal, due to an increase in temperature, the thermal velocities of free electrons also increase.
• Therefore, the number of collisions between free electrons and atoms increases. This increases the opposition to the movement of electrons and hence the resistance of the conductor.
• But this is not true for every material i.e., all materials do not have the same dependence on temperature.

Explanation:

• The number of conduction electrons is largely determined by the material's electronic configuration and does not significantly increase with temperature. Most metals have a vast 'sea' of delocalized electrons that exist regardless of a change in temperature. When a metal is heated, the thermal energy increases the kinetic energy of these existing electrons and causes them to collide more frequently with atomic cores, leading to increased resistance. It doesn't generate significantly more conduction electrons.
• Here's how it works: In metals, the conduction band (the energy band that conducts electricity) overlaps with the valence band (the band containing the outermost, or valence, electrons). Because of this overlap, the valence electrons can move freely between atoms. That's why metals are good conductors.
• If you heat a metal, you don't cause more electrons to jump into the conduction band because the bands overlap - the valence electrons are already conduction electrons.
• On the other hand, in semiconductors and insulators, there is an energy gap between the valence band and the conduction band. Heating can promote electrons across this gap, creating more conduction electrons and decreasing the resistance.
• To clarify, for a typical metal under standard conditions, Reason R: "The number of conduction electrons increases with temperature" is generally considered as not true. But for semiconductors and insulators at extremely high temperatures or under specific circumstances where more electrons can be promoted to conduction bands, the statement can be true.

 

Important Points

In metal, due to an increase in temperature, the thermal velocities of free electrons also increase.Most metals have a vast 'sea' of delocalized electrons that exist regardless of a change in temperature. 

Confusion Points

In metals, the conduction band (the energy band that conducts electricity) overlaps with the valence band (the band containing the outermost, or valence, electrons). Because of this overlap, the valence electrons can move freely between atoms. That's why metals are good conductors.​

If you heat a metal, you don't cause more electrons to jump into the conduction band because the bands overlap - the valence electrons are already conduction electrons.

Concept:

Resistance:

• It is a measure of the opposition to current flow in an electrical circuit.
• Resistance is measured in ohms, symbolized by the Greek letter omega (Ω).

In parallel combination of resistors: 

• Resistors are in parallel if their terminals are connected to the same two nodes.
• The equivalent overall resistance is smaller than the smallest parallel resistor.

• Formula, $\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}$

Calculation:

The total current, I = 1.2 A

The equivalent resistance of the circuit, $\frac{1}{R_{eq}}=\frac{1}{10}+\frac{1}{15}+\frac{1}{30}$

R_eq = 5 Ω 

The current I₂ can be calculated as,

$I_2=\frac{R_{eq}}{R_2}\times I$

$I_2=\frac{5}{15}\times 1.2=0.4A$

Additional Information

​In series combination of resistors:

• ​Two or more resistors are said to be connected in series when the same amount of current flows through all the resistors.
• In such circuits, the voltage across each resistor is different. In a series connection, if any resistor is broken or a fault occurs, then the entire circuit is turned off.

• Formula, Req = R1 + R2

Concept:

Bar magnet:

• It is a rectangular piece of an object that shows permanent magnetic properties and is made from a ferromagnetic substance.

​

Magnetic flux:

• Magnetic flux is a measurement of the total magnetic field which passes through a given area.

Lenz law:

• Lenz’s law depends on the principle of conservation of energy and Newton’s third law.
• It is the most convenient method to determine the direction of the induced current.
• It states that the direction of an induced current is always such to oppose the change in the circuit or the magnetic field that produces it.

Explanation:

• ​As the magnet falls the flux through the ring changes.
• Regardless of whether the flux increases or decreases, by Lenz's law a current is induced in the ring that opposes the change in flux.
• This induced current induced a magnetic field that interacts with the falling magnet and decreases the acceleration of fall below g.
• Hence, the acceleration of the falling magnet while passing through the ring is less than the acceleration due to gravity.

Concept:

Resistance:

• It is a measure of the opposition to current flow in an electrical circuit.
• It is measured in ohms, symbolized by the Greek letter omega (Ω).
• In the conducting wire, the resistance depends on the wire's length, cross-sectional area, and the material's resistivity.
• Formula, Resistance, $R=ρ \frac{l}{A}$, where ρ = resistivity of the material, A = cross-sectional area, l = length of the wire

Electrical Resistivity:

• It is a fundamental property of a material that measures how strongly it resists electric current.
• The SI unit of electrical resistivity is an ohm meter.

Calculation:

Let's consider the length of the wire is l and the radius of the wire is r.

The formula for the resistance of the conductor wire is given by,

$R=ρ \frac{l}{A}=ρ \frac{l}{\pi r^2}$ . . . . . . . . .  . . . . (1)

Now, the new length, l' = 2l

New radius, r' = 2r

So, $R'=ρ \frac{2l}{4\pi r^2}=ρ \frac{l}{2\pi r^2}$ . . . . . . .(2)

From equations (1) and (2), we get

$R'=\frac{R}{2}$

The electric resistivity of the wire remains the same.

Concept:

​Alloy Constantan:

• an alloy of 55 percent copper and 45 percent nickel.
• It is used in resistors, thermocouples, and rheostats.

Resistivity:

• The electrical resistance of a conductor of unit cross-sectional area and unit length.
• A characteristic property of each material, resistivity is useful in comparing various materials on the basis of their ability to conduct electric currents.
• High resistivity designates poor conductors.
• Low resistivity designates high conductors.

Temperature coefficient of resistivity:

• It is defined as the change in electrical resistance of a substance with respect to a per-degree change in temperature.
• The change in electrical resistance of any substance due to temperature depends mainly on three factors –
• The value of resistance at an initial temperature.
• The rise in temperature.
• The temperature coefficient of resistance α.
• The relation between the temperature and the resistance, R =  R₀ (1+α Δ T)

Explanation:

• The alloys manganin and constantan are used for making standard resistance coils as they have high resistivity, low-temperature coefficient of resistance, and the ability to attain good resistance values in small sizes.
• Their resistance value would change very little with temperature

Concept:

Gravitational potential energy:

• It is the energy possessed or acquired by an object due to a change in its position when it is present in a gravitational field.
• In simple terms, it can be said that gravitational potential energy is an energy that is related to gravitational force or to gravity.
• Formula, U = mgh, where m = mass, g = acceleration due to gravity, h = height
• The SI unit of the gravitational potential energy is Joule.

Power:

• It is defined as the work per unit of time.
• Formula, Power, $P=\frac{W}{t}$ where W = work done, t = time
• The SI unit of power is watt.

Calculation:

Given,

The mass of the Medha, m = 40 kg

The total vertical height, h = 24 × 20 = 480 cm = 4.8 m

Time, t = 1 min = 60 s

Acceleration due to gravity, g = 10 ms^-2

Work done, W = mgh

W = 40 × 10 × 4.8 = 1920 J

Power, $p=\frac{W}{t}$

$p=\frac{1920}{60}=32 , Watt$

Hence, the power expended by her is 32 watt.

Concept:

Hearing aid:

• Hearing aids are sound-amplifying devices designed to help people who have hearing loss.
• A hearing aid has three basic parts: a microphone, an amplifier, and a speaker.
• The hearing aid receives sound through a microphone, which converts the sound waves to electrical signals and sends them to an amplifier.
• The amplifier increases the power of the signals and then sends them to the ear through a speaker.
• In a hearing aid, the amplitude of the sound wave is changed.

Explanation:

• A sound wave's amplitude relates to the change in pressure caused by the wave measured at a specific location.
• The sound is perceived as louder if the amplitude increases, and softer if the amplitude decreases.
• So, in hearing aid, the amplitude of the sound wave changes and play an important role.

Concept:

• Echo: An echo is a sound caused by the reflection of sound waves from a surface back to the listener.
• It reflects sound, arriving at the listener sometime after the direct sound.

• The velocity formula for the echo is given as, $v=\frac{2d}{t}$ where d = distance between the source and reflectors, t = time taken to reflect back the echo.

Calculation:

Given,

Time, t = 1 s

The velocity of the sound in air, v = 340 ms^-1

Let's consider d is the distance between the man and the mountain.

The sound wave travels two times between the mountain and the man. 

So, $v=\frac{2d}{t}$

2d = vt

$d=\frac{vt}{2}$

$d=\frac{340\times 1}{2}=170 ~m$

Hence, the distance between the man and the mountain is 170m.

Concept:

Differences between elements and compounds - 

 

Explanation:

According to the given condition, two substances A and B react to form C,

A + B → C

→ In this reaction A and B reacts in a fixed proportion and  form another compound C

• A and can be either elements or compounds, which combine to give C.
• C is a compound as two different atoms combine to give C, it contains more than two different kinds of atoms.
• C is the result of a combination reaction.

Therefore, statement IV is correct.

Conclusion:

 Statement IV, " A and B may be elements or compounds and C is a compound" is correct only.

Hence, the correct answer is option 4.

Explanation:

Molecule and Compound -

Explanation:

→ A compound is,

• A substance is formed by two or more different types of elements that are bonded chemically in a fixed proportion.
• All compounds are molecules.
• They contain atoms of different chemical elements.
• A compound cannot be separated into its constituents by any physical means.
• A compound does not retain the physical properties of its constituent elements.
• Ex- NaOH (NaOH does not have individual physical characteristics of either Na or O or H).

∴ Statement I and statement II are correct.

Conclusion:

Therefore, statement III " A compound retains the physical properties of its constituent elements" is incorrect.

Hence, the correct answer is option 4.

Concept:

Sodium carbonate -

• Sodium carbonate is a salt of carbonic acid with the chemical formula Na2CO3.
• Sodium carbonate is also known as soda ash.
• It is a white powder and an odorless compound in pure form.
• Sodium carbonate is majorly produced by the Solvay process.
• It is a weak acid and a strong base.
• Its pH is 11.
• It is commonly known as washing soda and is used in cleaning products, glass production as a food additive, and more.

Explanation:

→ The valency of sodium (Na) is +1.

→ The valency or charge on carbonate ion (CO₃^2-)is -2.

To make a chemical formula, the valency of both should be balanced, so, for every carbonate ion there should be two sodium cation.

This can be shown as -

 

Conclusion:

The correct molecular formula for sodium carbonate is Na₂CO₃.

Therefore, the correct answer is option 2.

Concept:

Number of moles - 

1. A mole is a SI unit defined for the amount of substance.
2. It is the mass that a substance contains the same number of fundamental units such as atoms in 12g of C-12.
3. One mole of a substance is having N_A particles or atoms or molecules, where N_A is Avogadro's number.

Formula to calculate the number of moles,

Number of moles = $\frac{Given; weight; or;mass; of; the ; compound}{molecular ; mass ; of; the; compound}$ 

Calculation:

Number of moles = $\frac{Given; weight; or;mass; of; the ; compound}{molecular ; mass ; of; the; compound}$ ---------(1)

→ Nitrogen gas is having molecular formula N₂.

Its molecular mass is 28g\mole.

Given, a mole of N₂ = 0.5 mole 

Put all the values in equation (1),

∴ 0.5 = $\frac{ weight; or;mass; of; the ; compound}{28}$

Weight of the compound = 0.5 × 28 = 14g

Conclusion:

Hence, 0.5 moles of nitrogen gas is having 14g of nitrogen.

∴ the correct answer is option 2.

Concept:

​Equivalent weight -

Equivalent weight can be calculated as,

 Equivalent mass/wt. = $\frac{molecular; mass}{valency}$ 

Valency factor -

• Valency of an acid = basicity of the acid or no. of H⁺ ion
• Valency of a base = acidity of the base or the no. of OH^- ions
• Valency of a salt = charge on the ions

Calculation:

Equivalent mass/wt. = $\frac{molecular; mass}{valency}$

or molecular mass = Equivalent mass/wt. × valency ----------(1)

To calculate the molecular mass of X,

• If 'X" is a bivalent metal, its valency is 2.
• Given that it has an equivalent mass of 32.

Put all the values in equation (1), we get

the molecular mass of 'X' = Equivalent mass/wt. × valency = 32 × 2 = 64

∴ the molecular mass of 'X' = 64 g

The nitrate salt of metal X should be X(NO₃)₂ as X is bivalent and NO₃^- is a unipositive ion.

Molecular mass of X(NO3)2 = 64 + (14 +16 × 3)× 2 = 64 + (14+48)× 2 = 64 + 124 = 188

Conclusion:

∴ The molecular mass of the nitrate salt of this metal ‘X’ would be 188.

Hence, the correct answer is option 3.

Concept:

Oxides - 

Oxides are the compound of oxygen with other elements in which the oxidation state of 'O' is -2.

• Oxide is generally an anion of oxygen with oxidation number -2 or simply it is O2-.
• For example; NO, MgO. Na2O, etc.

Oxides are classified into four categories based on their acid-base characteristics. These are - 

1. Acidic oxides -

• Generally, the oxides of non-metals are acidic in nature and are called acidic oxides.
• In these oxides, atoms are held together by a covalent bond.
• For example; CO2, SO2, etc.

2. Basic oxides -

• ​​The metal reacts with oxygen to give basic oxides.
• Atoms of metal and oxygen are held by ionic bonds because of the large electronegativity difference.
• For example; MgO, Na2O, etc.

3. Amphoteric oxides -

• ​​Amphoteric oxides are those which can behave as acid and base.
• They can react with acid and base or they have the characteristics of both types of oxides acidic and basic.
• Al2O3 is amphoteric oxide.

4. Neutral oxides -

• ​​Neutral oxides are neither acidic nor basic.
• They neither show acidic characteristics nor show basic characteristics, simply they are neutral in nature.
• NO, and CO is examples of neutral oxides of oxygen.

Explanation:

Oxides can be acidic or basic or both or they can be neutral also, based on the characteristics they are showing in the solution.

Out of the given oxides,

→ Na2O

• Sodium is alkaline earth metal.
• Hence, its oxides of it are basic in nature.
• So, Na2O = Basic oxide

→ CaO

• CaO is a metal oxide.
• On reacting with water it produced a strong base.
• Its oxides are neutral in nature.
• So, CaO = Basic oxide

→CuO

• Cu(II) dissolved in water and produced hydroxide ions or forms Cu(OH)₂.
• It is a metallic oxide which is basic in nature
• So, CuO = Basic oxide

→ Al2O3

• Al can react with both acid as well as the base.
• Its oxides are amphoteric in nature.
• So, Al2O3 = Amphoteric oxide

Conclusion:

Therefore, Al2O3 is an Amphoteric oxide.

Hence the correct answer is option 4.

Concept:

Chemical and Physical change -

Explanation:

1. Burning of magnesium in the air is a chemical change as magnesium reacts with oxygen to form magnesium oxide.
2. Tarnishing of the silver spoon is a chemical change as silver forms a layer of silver sulphide.
3. The electrolysis of water is a chemical change as water breaks into ions.
4. Sublimation of iodine is only a physical change as only the state of iodine is changed from solid to gas without altering its composition.

Conclusion:

Therefore, the Sublimation of iodine is not a chemical change.

Hence, the correct answer is option 4.

Concept:

Redox reactions - These are reduction-oxidation chemical reactions.

• In these reactions, reactants undergo a change in their chemical oxidation states.
• These reactions are always accompanied by the reduction and oxidation of the reactants simultaneously.
• In oxidation, the Removal of hydrogen from a molecule or the addition of oxygen to a molecule takes place.
• In reduction, the Addition of hydrogen and removal of oxygen from a molecule takes place.
• Example of redox reaction, CH₄ + 2O₂ → CO₂ + 2H₂O

Explanation:

In oxidation, the Removal of hydrogen from a molecule or the addition of oxygen to a molecule takes place.

In reduction, the Addition of hydrogen and removal of oxygen from a molecule takes place.

This can be done by using an oxidizing agent or a reducing agent.

In the given reaction**,** H2S + Cl2 → 2 HCl + S

• H₂S  $\xrightarrow {-H_2}$  S (removal of hydrogen hence oxidation or H₂S is oxidized to S)
• Cl₂ $\xrightarrow {+H2}$ 2HCl (addition of hydrogen hence reduction or Cl₂ is reduced to HCl)

Conclusion:

Therefore, In the reaction H2S + Cl2 → 2 HCl + S, H2S is oxidized and Cl2 is reduced.

Hence, the correct answer is option 1.

Concept:

Exothermic process - 

• Exothermic reactions are those in which energy is released in form of heat or light.
• ΔH i.e enthalpy change for exothermic reactions is always negative.
• Burning of wood and dilution of an acid is the examples of exothermic reactions or processes.

Explanation:

The correct method for diluting an acid is adding acid to water with the following instructions -

1. Acid should be added dropwise.
2. acid should be added slowly.
3. A continuous and constant stirring is provided to the solution while adding the acid.

The precaution must be followed while mixing acid with water because the reaction of mixing acid to water is an exothermic process,

• Exothermic reactions are accompanied by releasing heat.
• The heat released in the reaction is very large.
• If water is added to acid, the heat released is such large that the flask can be broken and you will also suffer a serious injury.

Conclusion:

Thus, while diluting an acid, acid should be added slowly with constant stirring.

Hence, the correct answer is option 1.

Concept:

pH of a solution - 

• The pH of a solution indicates whether the solution is acidic or basic.
• It is the measure of hydrogen ion concentration in the solution.
• It ranges from 0 to 14.
• An acidic solution will have a higher concentration of hydrogen ions and a basic solution will have a higher concentration of OH- ions.
• The pH of the acidic solution lies between 1-7 on the pH scale and that of basic solutions lies between 7-14 on the pH scale.
• The more acidic the solution is lower is the pH of the solution.
• It is measured by using the formula, pH = -log[H+].

Explanation:

→ The higher the pH value for an acid, the weaker is the acid.

→ The higher the pH value for a base the stronger is the base.

The given table is 

• The pH of A is 1.5 and that of C is 4.5, pH of A is lower than that of C, hence A is a strong acid than C.
• The pH of B is 7.2 and that of D is 12.5, pH of D is higher than that of B, hence D is more basic than B.
• The highest pH is of D i.e. 12.5, hence from the given table, D is the most basic.
• The pH of C is 4.5 i.e <7 and that of E is 9.2 i.e >7, pH of C is lower than that of E and hence E is more basic than C.

Conclusion:

Therefore, statement I and statement III are correct only.

Hence the correct answer is option 1.

Concept:

• Soaps and detergents - Soap is a sodium or potassium salt of long-chain fatty acids, known for their cleansing action.
• A detergent is a surfactant having cleansing properties even in hard water.
• Plaster of Paris - It is Gypsum plaster. The chemical formula for the plaster of pairs is CaSO4. $\frac{1}{2}$ H2O.
• Disinfectants - a disinfectant is an antimicrobial agent usually applied on surfaces of objects to kill or destroy microorganisms.
• Antacids - Antacids are chemical substances used to neutralize the excess acid released in the stomach.
• Hardness of water - The hardness of water is due to the presence of Magnesium or calcium ions in water which restricts the cleansing action of soap.

Explanation:

Soaps and detergents -

• Soap is a sodium or potassium salt of long-chain fatty acids, known for their cleansing action.
• A detergent is a surfactant having cleansing properties even in hard water.
• Soap is manufactured by saponification reaction.
• NaOH is used in saponification reaction for the manufacturing of soaps and detergents.

Plaster of pairs(POP)-

• Plaster or Paris is a white powdered Chemical compound.
• It is hydrated calcium sulfate or calcium sulphate hemi-hydrate.
• It has the chemical formula CaSO4. $\frac{1}{2}$ H2O.
• It is used in putting casts on fractured bones in hospitals.

Disinfectants -

• A disinfectant is an antimicrobial agent usually applied on surfaces of objects to kill or destroy microorganisms.
• It is applied on non-living objects.
• We can use the same chemical as a disinfectant and an antiseptic by changing the concentration.
• Ex- Bleaching powder is used as water disinfectant having formula CaOCl₂.

Antacids -

• Antacids are the chemical substances used to neutralize the excess acid release in stomach.
• It is generally a base that neutralises the excess acid in the stomach.
• Ex- sodium bicarbonate, magnesium hydroxide, etc.

Hardness of water -

• Hardness of water is due to the presence of Magnesium or calcium ions in water which restricts the cleansing action of soap.
• Hardness of water is of two types -
• Permanent
• Temporary
• Permanent hardness can be removed by adding sodium carbonate or washing soda because it dissolves the insoluble carbonate that can be removed by filtration.

Conclusion:

Matching them accordingly, we get -

 

 

or a - iii, b - iv, c - v, d - ii, e - i.

Hence the correct t answer is option 2.

Concept:

​Decomposition reaction - 

• The reaction in which a single compound is broken down into two or more products is known as the decomposition reaction.
• The major application of decomposition reaction is obtaining the mineral from its ore.
• When decomposition is done with the help of heat, the reaction is known as the thermal decomposition reaction.

A common example of a decomposition reaction is an electrolytic breakdown of water into H2& O2

2H₂O → 2H₂ +O₂

Explanation:

→ Limestone is Calcium carbonate(CaCO₃).

→ Quick lime is Calcium oxide(CaO).

According to the given statement-‛‛Limestone decomposes on heating to give quick lime’’.

The decomposition of limestone CaCO₃ gives Calcium oxide(CaO) and carbon dioxide gas is released.

This is done by means of heat, thus the reaction is also called as thermal decomposition of limestone.

The chemical reaction is -

 CaCO3 (s) $\xrightarrow{Heat}$ CaO (s) + CO2 (g)

Conclusion:

The exact chemical reaction for the thermal decomposition of limestone to produce quick lime is -

CaCO3 (s) $\xrightarrow{Heat}$ CaO (s) + CO2 (g)

Thus, the correct answer is option 2.

Concept:

How metal reacts with water -

1. Metals react with water to give metal oxide and hydrogen gas.
2. Metal oxide soluble in water dissolves in water and produce hydroxides.
3. All metals do not react with water.
4. Sodium and potassium metals react vigorously with cold water.

General chemical reaction for the reaction of metals with water can be shown as - 

Metal + Water → Metal oxide + Hydrogen gas

Metal oxide + Water → Metal hydroxide 

Explanation:

→Metals react with water to give metal oxide and hydrogen gas.

Metal + Water → Metal oxide + Hydrogen gas 

Metal oxide + Water → Metal hydroxide 

All metals do not react with water in same way, as-

1. Metal that reacts violently with cold water - Sodium and Potassium
2. Metal that  floats on the water on reacting with water - Calcium (As bubbles due to hydrogen gas get stuck on the metal surface)
3. Metal that reacts with hot water only - Magnesium reacts with hot water only
4. Metal that reacts with steam only - Aluminium, Iron, and Zinc react with steam only and produce their oxides and hydrogen gas.
5. Metal that does not react with water at all - Lead, Copper, Silver and Gold

As per the options, A, B, C, D, E respectively are Potassium, Calcium, Magnesium, Aluminium, and Copper.

Conclusion:

 A, B, C, D, E respectively are Potassium, Calcium, Magnesium, Aluminium, Copper.

Hence, the correct answer is option 2.

Concept:

Chemical indicator - 

1. The chemical indicator is the substance that provides us an indication of whether the given solution has acidic or basic composition.
2. indicators generally change their colour or odour with a change in pH of the solution they are mixed with.
3. The most common application of indicators is in titrations, to note down the endpoint of the situations.
4. Ex-  methyl orange

Types of chemical indicators-

1. Natural indicators - These are obtained directly from nature. Ex- Turmeric
2. Synthetic indicators - They are made from synthetic chemicals in laboratories. Ex- Litmus indicator
3. Olfactory indicators- are those whose odour or smell changes according to the change in pH. Ex - Onion extract and vanilla extract

Explanation:

→ Olfactory indicators are those whose odour or smell changes according to the change in pH or according to acidic or basic medium.

Vanilla extract or essence changes its smell when mixed with acid or base.

• It is an olfactory indicator.
• It changes its smell according to how it reacts with acid or base.
• It has a pungent smell in an acidic medium and it is odourless in a basic medium.

Therefore, Vanilla essence is used as a chemical olfactory indicator to describe whether a given mixture is acidic or basic.

Hence, the correct answer is option 3.

Concept:

Dehydration of alcohol - 

• The dehydration of alcohol is done in presence of hot concn. sulphuric acid.
• Dehydration of alcohol in presence of hot concn. sulphuric acid gives the corresponding alkene.
• As the name dehydration indicates, the water molecule is removed from the alcohol.

The reaction mechanism can be shown as- 

 

Explanation:

1) CH3 CH2 OH + Na → CH3 CH2 O^- Na⁺ (sodium ethoxide)+ H⁺

• When ethanol is heated with sodium the ethoxide ion is formed.

2) CH3 CH2 OH 

CH2=CH2 (ethene) + H₂O

• This is dehydration of alcohol in presence of hot concn. sulphuric acid.
• Dehydration of alcohol in presence of hot concn. sulphuric acid gives the corresponding alkene.
• In the above reaction ethanol is dehydrated with hot concn. sulphuric acid and thus the product formed is ethene.

3)CH3 CH2 OH + CH3 COOH $\xrightarrow{acid}$ CH3 COO CH2 CH3 (ethyl acetate) + H₂O

• The reaction is called the Esterification reaction.
• Ethanol and ethanoic acid react in presence of an acid to give ethyl acetate.
• The product thus formed is an ester, that's why the creation is named as an esterification reaction.

4)CH3 CH2 OH 

CH3 COOH (acetic acid)

• KMnO₄ is a strong oxidising agent.
• It oxidised ethanol to ethanoic acid.

Conclusion:

Therefore, ethanol when dehydrated with hot concn. sulphuric acid the product formed is ethene.

CH3 CH2 OH 

CH2=CH2 (ethene) + H2O

Hence the correct answer is option 2.

Concept:

IUPAC Nomenclature-

• IUPAC stands for International Union for Pure and Applied Chemistry.
• It gives a systematic method for naming organic compounds.
• The rule decides the naming of an organic compound is known as the IUPAC rules.

Explanation:

IUPAC Nomenclature-

1. The total number of carbon present in the structure is 3 so, it has given a rootword 'prop'.
2. -CHO group is used a functional group, so, 'al' is used as 2°  suffix.
3. The given structure is having only C-C single bonds, therefore, it is a saturated alkane, thus using 'ane' as 1° suffix.

Thus, Prop + ane + al = Propanal

​

Conclusion:

 

The name of the compound represented by the formula 

is propanal.

 

Hence, the correct answer is option 3.

Concept:**

Addition reactions -

1. Unsaturated hydrocarbons undergo addition reaction with hydrogen in presence of catalysts such as Ni or Palladium to give a saturated hydrocarbon.
2. The reaction is also known as the hydrogenation reaction.
3. Hydrogenation is used to convert unsaturated oils and fats to saturated oils and fats.

The reaction can be shown as -

C2H4   $\xrightarrow{H_2, ;Ni ;or; Pd}$   C2H6  

Explanation:

Only unsaturated hydrocarbons undergo addition reaction.

Classification of given hydrocarbons as saturated or unsaturated hydrocarbon -

1. C2H6 (CnH2n+2) - Alkane (saturated)
2. C3H8 (CnH2n+2) - Alkane (saturated)
3. C3H6(CnH2n) - Alkene (Unsaturated)
4. C2H2(CnH2n-2) - Alkyne (Unsaturated)
5. CH4 - Methane - Alkane (Saturated)

Only C3H6, C2H2 are unsaturated hydrocarbons and hence only they will show addition reaction.

Conclusion:

Only C3H6, C2H2 are unsaturated hydrocarbons and hence only they will show addition reaction.

Hence, the correct answer is option 3.

Concept:

On moving left to right in a period,

• The principal shell remain same but atomic number is increasing as we move left to right in period.
• With increase in atomic number nuclear charge is increasing.
• With increase in atomic number, electrons  in the valence shell is also increasing.
• Therefore effective nuclear charge is increasing.
• Due to increased effective nuclear charge, the valence electrons or valence shell feels more pull to the nucleus.
• and atomic size reduces at every step in a period (general trend).

Explanation:

→  Metallic character in a period,

• Metallic character decreases as we move left to right in a period as the tendency to lose electrons decreases from left to left.
• Thus the elements become less metallic from left to right in a period.

→ Valence electrons in a period,

• With an increase in atomic number, electrons in the valence shell are also increasing.
• Therefore effective nuclear charge is increasing.

→ Atomic size in a period, 

• Due to increased effective nuclear charge, the valence electrons or valence shell feels more pull to the nucleus.
• and atomic size reduces at every step in a period (general trend).
• It becomes difficult to lose electrons by an atom as size is reduced in a period.

→ Nature of oxides,

• Oxides of alkali and alkaline earth metals are more basic as they are present on the left side of the periodic table.
• basic nature of the oxides decreases as we move left to right in a period.
• Therefore, the acidic nature of oxides increases in a period from left to right.

Conclusion:

Statement III, " The atoms lose their electrons more easily" is incorrect as it becomes difficult to lose electrons by an atom as atomic size is decreasing over a period.

 

Hence, the correct answer is option 3.

Concept:

Ionic compound - 

• Ionic compounds are usually formed when a metal reacts with a non-metal.
• Ionic compounds are held together by ionic bonds.
• NaCl is an example of an ionic compound.

Explanation:

→ Element 'A' belong to group 1, period 3 indicates

• 'A'  is an alkali metal.
• It belongs to group 3 i.e. it must be Na.
• An element belonging to group 1 is having valency 1.

→ Element 'B' belongs to group 17 and period 3 indicates - 

• Element 'B' must be a halide, especially chlorine (Cl).
• Its valency is also 1.

To make a chemical formula, the valency of both should be balanced.

Na and Cl react to give NaCl as -

Conclusion:

As both A and B have the same valency, they must form a compound C which can be represented by the formula AB. 

Hence the correct answer is option 2.

Concept:

Atomic radius - It is the distance from the center of the nucleus to the outermost shell containing electrons. Atomic size is measured in terms of atomic radius.

Atomic radius basically is of three types -

1. Covalent radius
2. Van der Waal's radius
3. Metallic radius

Variation of atomic radius in a period - In a period generally atomic radius decreases with an increase in atomic number or atomic radius decreases as we move left to right in a period.

Variation of atomic radius in a period - in a group, generally atomic radius increases as we move down in a group from top to bottom.

Explanation:

According to the variation of atomic radius in a period, the atomic radius decreases as we move left to right in a period.

Reason - 

In a period,

• The principal shell remains the same.
• As we move left to right, the atomic number increases.
• With an increase in atomic number, the number of valence electrons increases.
• so, effective nuclear charge also increases.
• Due to increased effective nuclear charge, the valence electrons or valence shell feels more pull to the nucleus.

Therefore, the atomic radius decreases in a period because effective nuclear charge increases with the addition of each electron in the valence shell.

Conclusion:

Both A and R are true and R is the correct explanation of A.

Hence, the correct answer is option 1.

Concept:

Esterification reaction - 

• It is a reaction between an organic acid (RCOOH) with a primary alcohol(ROH) in presence of an acid to give an ester.
• The reaction is named as esterification as an ester is formed as a result of the reaction.
• It can be represented as - RCOOH + R'OH $\xrightarrow {Acid}$  RCOOR' (Ester)+ H₂O
• The esterification reaction is widely used in the manufacturing of ester for medicinal purposes.
• The esterification reaction is the reverse of the saponification reaction.

Explanation:

Identify ‘A’ in the following reaction :

A + C2H5OH $\xrightarrow{Acid}$ $\rm \begin{matrix}\rm CH_3-C-O-C_2H_5 \\ ||\rm \\ \rm O\\ \rm \\\ \end{matrix}$

The given reaction is an Esterification reaction.

→Esterification reaction of carboxylic acid and alcohol yields in the formation of an ester.

In the given reaction, the product is ethyl ethanoate or ethyl acetate, which is formed when acetic acid and ethanol react in the presence of an acid.

∴ 'A' in the given reaction must be acetic acid.

The complete reaction can be shown as  -

CH₃COOH (acetic acid )+ C₂H₅OH (ethanol) $\xrightarrow{Acid}$CH₃COOC₂H₅(ethyl acetate)

Conclusion:

Therefore,  'A' in the given reaction must be acetic acid or CH3COOH.

Hence, the correct answer is option 2.

Concept:

Tarnishing of silver - 

• Tarnishing means the fine layer of corrosion on a metal surface.
• Silver tarnishing happens due to the formation of silver sulphide on the surface of the silver.
• Due to the layer of silver sulphide on the silver surface, the colour of the silver turns dark or black.
• The reason of silver tarnishing is the exposure of the silver to the air.
• To avoid silver tarnishing, silver items should be cleaned with soap water and ammonia solution.

Explanation:

Silver items become black after some time when exposed to air.

→ The reason behind the black colour of silver is the formation of silver sulphide on the silver surface.

• Silver reacts with sulphur compounds present in the air such as H₂S and silver sulphide is formed.

The reaction can be shown as -

2Ag  + H₂S → Ag₂S ↓  + H₂

Conclusion:

Thus, the black colour substance formed is due to silver sulphide.

Hence, the correct answer is option 3.

Concept:

Metallurgy - 

The process which involved the extraction of pure metal from naturally occurring ores is called metallurgy.

To extract the metal in its pure form a number of steps are done. These include -

• Crushing and grinding of the ore.
• The concentration of the ore.
• Extraction of crude metal.
• Purification of the metal

There are some common terms used in metallurgy like minerals, ores, gangue\matrix, etc.

Explanation: 

Concentrated ores can be converted into their oxides by the process of calcination or roasting. 

→ Calcination is the process of conversion of carbonate ores into metal oxide by strongly heating in the limited supply or absence of air.

• Siderite is the carbonate ore of iron and thus can be converted it into its oxide by calcination.
• In this process, FeCO3 is heated strongly below its melting point in the absence of air.
• The chemical reaction is -  FeCO3  → FeO + CO2

→ Roasting is the process of conversion of sulfide ores into metal oxide by heating strongly in presence of air.

Conclusion: Carbonated ores are converted into oxides by heating strongly in the absence of air. This process is known as Calcination.

Therefore, A, B, and C are carbonated, absent and calcination respectively.

Hence, the correct answer is option 2.

Concept:

Balance a redox reaction -

1. Write down the chemical equation.
2. Write the oxidation number for each element.
3. Write the half-reactions for elements of interest.
4. Balanced each half-reaction on both sides according to the -
5. Balance the element of interest
6. Balance O atoms by adding H₂O
7. Balance H atoms by adding H⁺
8. Balance electronic charge by adding electrons
9. Balance the overall equation for electrons.
10. Add half-reactions and simplify

Explanation:

For the above reaction to balance follow the steps - 

1. Write down the chemical equation.
2. Write the oxidation number for each element.
   

3. Write the half-reactions for elements of interest. 4. Balanced each half-reaction on both sides according to the -

1. Balance the element of interest
2. Balance O atoms by adding H2O
3. Balance H atoms by adding H+

Balance electronic charge by adding electrons

                    Oxidation half

                     2 × [2AI + 3H₂O] → 2 × [Al₂O₃ + 6H⁺ + 6e^- ]

                     4Al + 6H₂O → 2Al₂O₃ + 12 H⁺ + 12e^-

                    Reduction half

                    3 × [ Mno₂ + 4H⁺ + 4e^-] → 3 × [ Mn + 2H₂O]

                   3MnO₂ + 12H⁺ + 12e^- → 3Mn+6H₂O

1. Balance the overall equation for electrons.

2. Overall:- 4Al + 6H₂O + 3MnO₂ + 12 H⁺ + 12e^- → 2AI₂O₃ + 12H⁺ + 12e^- + 3Mn + 6H₂O 3. Add half-reactions and simplify

Conclusion:

For the above reaction to be balanced, the values of x, y, z are 3, 4, and 2 respectively.

Therefore the correct answer is option  2.