General Science PYQs

The correct answer is Red blood cells.

Key Points

• A tissue is a group of similar cells that work together to perform a specific function. The study of tissues is known as Histology.
• Nerves are primarily composed of nervous tissue, which consists of neurons (nerve cells) and neuroglia. They are responsible for transmitting electrical impulses throughout the body. Hence, statement 1 is a tissue.
• Red blood cells (Erythrocytes) are individual cells produced in the bone marrow. While they are a major component of blood, they are considered single cells rather than a tissue on their own. Hence, statement 2 is NOT a tissue.
• Muscles consist of muscular tissue, which is characterized by the ability to contract and relax, enabling movement. It is one of the four primary tissue types in animals. Hence, statement 3 is a tissue.
• Blood is uniquely classified as a fluid connective tissue. It is considered a tissue because it consists of a group of specialized cells (RBCs, WBCs, and platelets) that originate from a common source and function together within the plasma. Hence, statement 4 is a tissue.

Additional Information

• Types of Animal Tissues:
• Epithelial Tissue: Acts as a protective layer covering the body surface and lining internal organs (e.g., skin, inner lining of the mouth).
• Connective Tissue: Supports, binds, and protects other tissues and organs. Examples include bone, cartilage, tendons, and blood.
• Muscular Tissue: Responsible for locomotion and movement. It is divided into skeletal, smooth, and cardiac muscles.
• Nervous Tissue: Forms the brain, spinal cord, and nerves. It specialized in communication using electrochemical signals.
• Red Blood Cells (RBCs):
• They are biconcave in shape and lack a nucleus at maturity in humans to provide more space for hemoglobin.
• Their primary function is the transport of oxygen from the lungs to the tissues and carbon dioxide back to the lungs.
• The average lifespan of a human RBC is approximately 120 days.

Important Points

• Levels of Organization: In biological systems, the hierarchy of complexity begins with the cell (the basic unit of life). A group of cells forms a tissue, multiple tissues form an organ (like the heart or lungs), and organs work together in an organ system (like the circulatory system).
• Why Blood is a Tissue: Although liquid, blood meets the criteria for a tissue because it has a matrix (plasma) and specific cellular components (erythrocytes, leukocytes, and thrombocytes) that work collectively for transportation, protection, and regulation.
• Histology Origins: The term "tissue" was introduced by Marie François Xavier Bichat in the late 18^th century, who is often regarded as the Father of Histology.

The correct answer is Hydrogen.

Key Points

• The given chemical equation CuO + H2 → Cu + H2O represents a classic redox (reduction-oxidation) reaction where both oxidation and reduction occur simultaneously.
• Oxidation is defined as the chemical process where a substance gains oxygen or loses hydrogen. In this reaction, the Hydrogen (H2) molecule reacts with Copper oxide (CuO) and gains an oxygen atom to form Water (H2O).
• Because Hydrogen is the species that acquires oxygen during the chemical change, it is the substance that is oxidised.
• Reduction, conversely, is the process where a substance loses oxygen or gains hydrogen. Here, Copper oxide (CuO) loses its oxygen atom to be converted into metallic Copper (Cu).
• Since Copper oxide undergoes the loss of oxygen, it is identified as the substance being reduced in this chemical interaction.

Additional Information

• Oxidizing and Reducing Agents:
• An oxidizing agent is a substance that facilitates oxidation by providing oxygen or accepting electrons. In this reaction, Copper oxide (CuO) is the oxidizing agent because it provides the oxygen required for the oxidation of hydrogen.
• A reducing agent is a substance that facilitates reduction by removing oxygen or donating electrons. Hydrogen (H2) acts as the reducing agent here because it removes the oxygen from the copper oxide.
• Electronic Concept of Redox:
• In modern chemistry, oxidation is also defined as the loss of electrons (increase in oxidation state), while reduction is the gain of electrons (decrease in oxidation state).
• In the reaction CuO + H2 → Cu + H2O, the Copper ion in CuO has an oxidation state of +2 and is reduced to 0 in metallic Cu. The Hydrogen atom has an oxidation state of 0 in H2 and is oxidised to +1 in H2O.
• Applications of Redox Reactions:
• These reactions are fundamental to metallurgical processes, such as the extraction of metals from their ores (e.g., using carbon or hydrogen to reduce metal oxides).
• They are also essential in biological systems for energy production (cellular respiration) and in everyday phenomena like combustion, rusting of iron, and the functioning of batteries.

Important Points

• Nature of the Reactants: Copper oxide (CuO) is typically a black solid, while metallic Copper (Cu) formed after reduction appears as a reddish-brown substance. This visible change in color is a key indicator that a chemical reaction has taken place.
• Role of Heat: This specific reaction generally requires heating the copper oxide in a stream of hydrogen gas to proceed at a measurable rate, making it an endothermic process in terms of activation energy.
• Water Formation: The Water (H2O) produced in this reaction is often released in the form of steam or water vapor due to the heat applied during the process.
• Hydrogen as a Reducer: Hydrogen is a powerful reducing agent capable of reducing the oxides of many metals that are less reactive than hydrogen in the reactivity series, such as lead, silver, and copper.

The correct answer is It is always greater than 1.

Key Points

• The absolute refractive index of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in that specific medium.
• It is mathematically expressed by the formula n = c / v, where n is the absolute refractive index, c is the speed of light in a vacuum (approximately 3 x 10^8 meters per second), and v is the speed of light in the medium.
• According to the laws of physics, light travels at its maximum speed in a vacuum. In any other material medium (like water, glass, or oil), light interacts with atoms and slows down, meaning the value of v is always less than c.
• Because the numerator (c) is always larger than the denominator (v), the ratio will always result in a value greater than 1 for all physical media. Hence, statement 1 is correct.
• The refractive index of a vacuum is exactly 1. For all other substances, it is higher. For example, the refractive index of air is about 1.0003, which is extremely close to 1 but still greater. Hence, statement 2 is incorrect.
• The refractive index represents a ratio of two speeds, which means the units cancel out, making it a dimensionless and unitless quantity. Hence, statement 4 is incorrect.
• In natural materials, the refractive index is always positive. While scientists have engineered "metamaterials" that can have a negative refractive index under specific lab conditions, in the context of standard optics, it is not negative. Hence, statement 3 is incorrect.

Additional Information

• Optical Density: A medium with a higher refractive index is referred to as optically denser, whereas a medium with a lower refractive index is optically rarer. When light enters a denser medium, its speed decreases and it bends toward the normal.
• Common Refractive Indices:
• Water: Approximately 1.33.
• Crown Glass: Approximately 1.52.
• Diamond: Approximately 2.42, which is one of the highest among natural substances, contributing to its extreme sparkling and total internal reflection.
• Snell's Law: The refractive index is used in Snell's Law of Refraction, which states that n1 sin(i) = n2 sin(r), where i is the angle of incidence and r is the angle of refraction.
• Relative Refractive Index: This refers to the ratio of the speed of light in medium 1 to the speed of light in medium 2. Unlike the absolute refractive index, a relative refractive index can be less than 1 if light moves from a denser medium to a rarer one.
• Factors of Influence: The refractive index of a material depends on the temperature, the nature of the material, and the wavelength of light (a phenomenon known as dispersion, which causes rainbows).

Important Points

• Speed of Light: In a vacuum, light travels at 299,792,458 meters per second. For general calculations, this is rounded to 3 x 10^8 m/s.
• Relationship with Wavelength: Since the frequency of light remains constant when changing media, a change in speed results in a change in wavelength. The refractive index is also the ratio of the wavelength in a vacuum to the wavelength in the medium (n = λ_vacuum / λ_medium).
• Significance: The concept of refractive index is vital in designing lenses, microscopes, telescopes, and fiber optic cables used in modern high-speed internet.

The correct answer is v = (s2 - s1)/(t2 - t1).

Key Points

• The speed of an object is defined as the rate of change of distance with respect to time. Mathematically, it is expressed as v = Distance / Time.
• On a distance-time graph, the distance (s) is typically represented on the vertical axis (y-axis), and the time (t) is represented on the horizontal axis (x-axis).
• When an object moves from point A to point B, the change in distance is given by (s2 - s1), which represents the total path length covered between those two points.
• The duration or time interval taken to cover this distance is calculated as (t2 - t1).
• The slope of the line joining points A and B on a distance-time graph represents the speed (v) of the object. Therefore, the formula is v = (s2 - s1) / (t2 - t1). Hence, the statement represented by option 1 is correct.
• The unit of speed in the International System of Units (SI) is meters per second (m/s), although it is often expressed in km/h for vehicles.

Additional Information

• Uniform and Non-Uniform Motion:
• In uniform motion, an object covers equal distances in equal intervals of time, resulting in a straight line on a distance-time graph.
• In non-uniform motion, the distance-time graph is a curve, indicating that the speed is changing at different points in time.
• Speed vs. Velocity:
• While speed is a scalar quantity (only magnitude), velocity is a vector quantity that includes both magnitude and direction.
• The slope of a displacement-time graph gives the velocity, whereas the slope of a distance-time graph gives the speed.
• Instantaneous Speed:
• The speed of an object at any particular instant of time is called instantaneous speed. In a graph, this is found by calculating the slope of the tangent at that specific point.
• Average Speed:
• Average speed is the total distance traveled divided by the total time taken. The formula v = (s2 - s1) / (t2 - t1) effectively calculates the average speed between two specific time coordinates.

Important Points

• Graph Interpretation:
• If the distance-time graph is a horizontal line (parallel to the time axis), the speed is zero, meaning the object is at rest.
• A steeper slope on the graph indicates a higher speed, as more distance is being covered in less time.
• A distance-time graph can never have a negative slope because distance is a cumulative quantity that never decreases with time, unlike displacement.
• Mathematical Relations:
• The expression (s2 - s1) is often denoted as delta s (Δs) and (t2 - t1) as delta t (Δt). Thus, v = Δs / Δt.
• This relationship is fundamental in kinematics and is used to derive further equations of motion under constant acceleration.

The correct answer is Definite volume and shape under normal conditions.

Key Points

• Solids are defined by their structural rigidity and resistance to changes in shape or volume. Unlike liquids or gases, the constituent particles (atoms, molecules, or ions) in a solid are closely packed together.
• One of the most fundamental features of all solids is that they possess a definite shape and a definite volume. This is due to the strong intermolecular forces of attraction that hold the particles in fixed positions. Hence, statement 2 is correct.
• Solids are generally incompressible. Because the particles are already so close to each other, applying pressure does not significantly reduce the volume. Hence, statement 1 is incorrect.
• Solids do not have the ability to flow. Fluidity is a characteristic of liquids and gases, where particles can slide past one another. In solids, particles only vibrate around their mean positions. Hence, statement 3 is incorrect.
• While solids can expand when heated (thermal expansion), they do not have infinite expansion capability. This property is characteristic of gases, which expand to fill the entire volume of any container they occupy. Hence, statement 4 is incorrect.

Additional Information

• Classification of Solids:
• Crystalline Solids: These have a regular, repeating three-dimensional pattern of particles. Examples include diamond, quartz, and sodium chloride (salt). They typically have sharp melting points.
• Amorphous Solids: These lack a long-range ordered structure. Examples include glass, rubber, and many plastics. They soften over a range of temperatures rather than melting at a specific numerical value.
• Kinetic Molecular Theory:
• In the solid state, the kinetic energy of the particles is at its lowest compared to the liquid or gaseous states.
• The particles are held together by various types of bonds, such as ionic, covalent, metallic, or van der Waals forces.
• Physical Properties:
• Density: Most substances are at their highest density in the solid phase (ice is a notable exception due to its unique hydrogen bonding structure).
• Diffusion: The rate of diffusion in solids is extremely low because particles are not free to move across large distances.

Important Points

• Phase Transitions: The process of a solid turning into a liquid is called melting, while the direct transition from a solid to a gas is known as sublimation (e.g., dry ice or naphthalene).
• Elasticity vs. Plasticity: Some solids can be deformed under stress. If they return to their original shape, they are elastic; if the deformation is permanent, they are plastic.
• Mechanical Strength: Solids are categorized by their hardness, brittleness, and malleability (the ability to be hammered into thin sheets, a common feature of metals like gold and silver).

The correct answer is 3.

Key Points

• Bohr’s Model of an atom, proposed by Neils Bohr in 1913, postulates that electrons revolve around the nucleus in certain stable, circular paths called orbits or shells.
• These orbits are associated with fixed amounts of energy and are called energy levels or energy shells.
• The shells are represented by the letters K, L, M, N, ... or by the principal quantum number (n), where n is an integer (1, 2, 3, 4, ...).
• The shell closest to the nucleus is the K shell, for which n = 1. The next shell is the L shell with n = 2.
• The M shell is the third orbit from the nucleus, and thus it is represented by the principal quantum number n = 3. Hence, the statement regarding M shell being represented by n equal to 3 is correct.
• The N shell follows the M shell and is represented by n = 4.

Additional Information

• Maximum Electron Capacity: The maximum number of electrons that can be accommodated in a shell is calculated using the formula 2n², where n is the principal quantum number.
• For the K shell (n=1): 2(1)² = 2 electrons.
• For the L shell (n=2): 2(2)² = 8 electrons.
• For the M shell (n=3): 2(3)² = 18 electrons.
• For the N shell (n=4): 2(4)² = 32 electrons.
• Energy Levels: As the value of n increases, the distance of the shell from the nucleus increases, and the energy associated with that shell also increases. Therefore, the M shell has higher energy than the L shell but lower energy than the N shell.
• Stability: According to Bohr, electrons do not radiate energy while revolving in these discrete orbits. An atom radiates or absorbs energy only when an electron jumps from one energy level to another.
• Octet Rule: The outermost shell of an atom cannot accommodate more than 8 electrons, even if it has the capacity to hold more (except for the K shell, which holds a maximum of 2).
• Scientific Contribution: Neils Bohr was awarded the Nobel Prize in Physics in 1922 for his work on the structure of atoms. His model helped overcome the limitations of the Rutherford model regarding atomic stability.

The correct answer is menstrual cycle.

Key Points

• The menstrual cycle is a series of natural, rhythmic physiological changes that occur in the female reproductive system (specifically in primates like humans, monkeys, and apes) to make pregnancy possible.
• This cycle involves regular changes in both the ovary (production of eggs/ovocytes) and the uterus (preparation of the lining for a potential embryo).
• The average duration of a menstrual cycle is 28 days, although it can vary between 21 and 35 days in healthy adults.
• The cycle is characterized by the shedding of the uterine lining (endometrium), which results in menstruation (bleeding) if fertilization does not occur.
• It is regulated by the complex interplay of hormones from the hypothalamus, pituitary gland, and the ovaries.

Additional Information

• Estrous Cycle:
• Unlike the menstrual cycle, the estrous cycle occurs in non-primate mammals such as cows, dogs, and cats.
• In this cycle, the endometrium is reabsorbed by the body if fertilization does not take place, rather than being shed as blood.
• Animals with an estrous cycle are generally only sexually active during the "heat" or estrus phase.
• Circadian Rhythm:
• This refers to the 24-hour internal clock in our brain that regulates cycles of sleepiness and alertness.
• It responds primarily to light and darkness in an organism's environment and is not directly responsible for egg formation.
• Menarche and Menopause:
• Menarche is the term used for the first menstrual cycle, which typically occurs during puberty between the ages of 11 and 15.
• Menopause marks the end of reproductive phases in women, usually occurring between the ages of 45 and 55, where menstrual cycles cease permanently.
• Fertilisation cycle:
• This is not a standard biological term for the regular monthly changes; rather, fertilisation is a singular event where the sperm meets the ovum.

Important Points

• Phases of the Menstrual Cycle:
• Menstrual Phase (Days 1-5): The endometrium is shed, and menstrual flow occurs due to low levels of progesterone.
• Follicular Phase (Days 1-13): Follicle-stimulating hormone (FSH) stimulates the growth of ovarian follicles. The lining of the uterus regenerates.
• Ovulatory Phase (Day 14): A sudden surge in Luteinizing Hormone (LH) causes the mature follicle to rupture and release the egg (ovum). This process is called ovulation.
• Luteal Phase (Days 15-28): The ruptured follicle transforms into the corpus luteum, which secretes progesterone to prepare the uterus for implantation.
• Hormonal Control:
• Estrogen: Responsible for the proliferation of the uterine lining and secondary sexual characteristics.
• Progesterone: Essential for maintaining the thickened uterine lining during pregnancy.
• LH and FSH: Pituitary hormones that trigger the maturation of follicles and the act of ovulation.

p data-end="57" data-start="0">The correct answer is Virus.

 

Key Points

• AIDS stands for Acquired Immunodeficiency Syndrome. It is a chronic, potentially life-threatening condition caused by the Human Immunodeficiency Virus (HIV).
• By damaging the immune system, HIV interferes with the body's ability to fight infection and disease. It specifically targets and destroys CD4 cells (also known as T-helper cells), which are vital for the immune response.
• The causal agent of AIDS is a Virus. HIV is a member of the Retrovirus family, which means it uses RNA as its genetic material and employs an enzyme called reverse transcriptase to integrate into the host's DNA. Hence, statement 2 is correct.
• Helminths are multi-cellular parasitic worms, such as roundworms and tapeworms, that cause diseases like Ascariasis or Filariasis. They are not the cause of AIDS. Hence, statement 1 is incorrect.
• Protozoa are single-celled organisms that cause illnesses such as Malaria, Amoebiasis, and Kala-azar. They do not lead to the development of AIDS. Hence, statement 3 is incorrect.
• Bacteria are prokaryotic microorganisms responsible for diseases like Tuberculosis, Cholera, and Typhoid. While some sexually transmitted diseases (STDs) like Syphilis are bacterial, AIDS is not. Hence, statement 4 is incorrect.
• Hence, the correct answer is Virus.

Additional Information

• Modes of Transmission:
• HIV is transmitted through contact with infected blood, semen, or vaginal fluids. The most common route is unprotected sexual contact.
• It can also spread by sharing contaminated needles and syringes, or through blood transfusions if the blood has not been screened. Transmission from mother to child can occur during pregnancy, childbirth, or breastfeeding.
• Diagnostic Procedures:
• The primary screening test for HIV is the ELISA (Enzyme-Linked Immunosorbent Assay) test, which detects antibodies against the virus.
• A positive ELISA result is usually confirmed using a more specific test known as the Western Blot test. In recent years, p24 antigen tests and Nucleic Acid Tests (NAT) are also used for early detection.
• Stages of Infection:
• The infection progresses through stages: Acute HIV Infection, Clinical Latency (Chronic HIV), and finally AIDS, which is the most severe phase.
• A person is diagnosed with AIDS when their CD4 cell count drops below 200 cells/mm3 or when they develop certain opportunistic infections like Pneumocystis pneumonia or Kaposi's sarcoma.

Important Points

• Global and National Context:
• World AIDS Day is observed annually on December 1^st to raise awareness and mourn those who have died from the disease. It was first conceived in 1988.
• In India, the National AIDS Control Organisation (NACO), established in 1992, is the nodal agency for formulating policy and implementing programs for the prevention and control of HIV/AIDS.
• Treatment and Management:
• There is currently no cure for HIV/AIDS, but it can be managed with Antiretroviral Therapy (ART). ART involves taking a combination of medicines every day that prevent the virus from multiplying.
• Effective ART can reduce the viral load to undetectable levels, meaning the person can live a long life and has effectively no risk of transmitting the virus through sex.
• The incubation period (the time from infection to the development of AIDS) can range from 5 to 10 years or more depending on the individual's health and treatment status.

The correct answer is 640 m.

Key Points

• An echo is the phenomenon where a sound is heard again after it is reflected back from a distant obstacle, such as a cliff, a mountain, or a large wall.
• When a person claps their hands near a cliff, the sound travels from the person to the cliff and then reflects back to the person's ears. Therefore, the total distance covered by the sound is twice the actual distance between the person and the cliff.
• In this problem, the speed of sound (v) is given as 320 m/s and the time interval (t) for the echo to be heard is 4 s.
• The formula to calculate the distance is: Total Distance = Speed of Sound x Time. Here, Total Distance = 320 m/s x 4 s = 1280 m.
• Since this 1280 m represents the distance of the "to-and-fro" journey, the distance of the cliff (d) from the girl is half of the total distance.
• Calculation: d = 1280 / 2 = 640 m. Hence, the correct option is 640 m.

Additional Information

• Nature of Sound Waves: Sound is a mechanical wave that requires a medium (solid, liquid, or gas) to travel. It travels fastest in solids and slowest in gases.
• Speed of Sound: The speed of sound in air is approximately 344 m/s at a temperature of 22 degrees Celsius. The speed increases with an increase in temperature and humidity.
• Reflection of Sound: Just like light, sound follows the laws of reflection, where the angle of incidence is equal to the angle of reflection, and they lie in the same plane.
• Applications of Echo: The principle of echo is used in SONAR (Sound Navigation and Ranging) to measure the depth of the ocean or locate underwater objects. It is also used by bats and dolphins for echolocation to navigate and find food.
• Medical Use: Ultrasonography uses the reflection of ultrasonic waves (sound with frequency above 20,000 Hz) to create images of internal body organs.

Important Points

• Persistence of Hearing: The sensation of sound persists in our brain for about 0.1 seconds. To hear a distinct echo, the reflected sound must reach the ear after this time interval.
• Minimum Distance for Echo: For a person to hear a clear echo in air (at 22 degrees Celsius), the minimum distance of the obstacle from the source of sound should be half of the distance traveled in 0.1 s. Calculation: (344 m/s x 0.1 s) / 2 = 17.2 m.
• Reverberation: If the distance is less than 17.2 m, the reflected sounds overlap with the original sound, causing a prolonged sound effect known as reverberation, commonly heard in large concert halls or newly built empty rooms.
• Human Auditory Range: A healthy human ear can typically hear frequencies between 20 Hz and 20,000 Hz. Sounds below 20 Hz are called infrasonic, and sounds above 20,000 Hz are called ultrasonic.

The correct answer is Nucleus.

Key Points

• Protons are subatomic particles located deep within the center of an atom, in a region known as the nucleus.
• The nucleus is a small, dense, and positively charged core that contains nearly all of the atom's mass, despite occupying only a tiny fraction of its total volume.
• A proton carries a positive electrical charge of +1 elementary charge (approximately 1.602 × 10⁻¹⁹ Coulombs).
• The total number of protons in the nucleus defines the Atomic Number (denoted by Z) of an element, which determines its chemical identity and position on the Periodic Table.
• The discovery of the proton is credited to Ernest Rutherford, who through experiments conducted between 1917 and 1919, proved that the hydrogen nucleus was present in other nuclei.

Additional Information

• Neutrons:
• These are neutral subatomic particles (no charge) also found within the nucleus alongside protons.
• They were discovered by James Chadwick in 1932.
• Together, protons and neutrons are referred to as nucleons.
• Electrons:
• Unlike protons, electrons are found outside the nucleus in the electron cloud, arranged in specific orbitals or energy levels.
• They carry a negative electrical charge (-1e) and have a very small mass, approximately 1/1836^th the mass of a proton.
• They were discovered by J.J. Thomson in 1897 using the cathode ray tube experiment.
• Atomic Mass:
• The Mass Number (denoted by A) of an atom is the sum of the total number of protons and neutrons in its nucleus.
• The mass of a proton is approximately 1.00727 atomic mass units (amu).

Important Points

• Rutherford’s Gold Foil Experiment (1911): This landmark experiment led to the discovery of the nucleus. It showed that most of the atom is empty space, with a tiny, dense, positively charged center that deflected alpha particles.
• Quark Composition: Protons are not fundamental particles; they are composed of smaller particles called quarks. A proton consists of two Up quarks and one Down quark, held together by the strong nuclear force mediated by gluons.
• Nuclear Stability: The strong nuclear force is the fundamental force that overcomes the electrostatic repulsion between positively charged protons, allowing them to stay tightly packed within the nucleus.

The correct answer is Neither (i) nor (ii).

Key Points

• Acceleration due to gravity (g) is the acceleration gained by an object due to the gravitational force exerted by a massive body like the Earth. Its standard value on the Earth's surface is approximately 9.8 m/s².
• The mathematical formula for acceleration due to gravity is g = GM / R², where G is the Universal Gravitational Constant, M is the mass of the Earth (or the celestial body), and R is the radius of the body.
• Statement

(i) claims that g depends on the mass of the falling object. However, the formula g = GM / R² shows that the acceleration depends only on the mass and radius of the planet, not the object. In a vacuum, a feather and a hammer will fall at the same rate. ***Hence, statement

(i) is incorrect.***

• Statement

(ii) claims that g is universally constant. This is false because g varies based on location. It is maximum at the poles and minimum at the equator due to the Earth's oblate spheroid shape. It also decreases with an increase in altitude (height above Earth) and depth (below Earth's surface). ***Hence, statement

(ii) is incorrect.***

• Since neither of the statements provided in the question is factually accurate regarding the properties of g, the correct option is Neither (i) nor (ii).

Additional Information

• Difference between g and G:
• g is the acceleration due to gravity, which is a vector quantity and changes from place to place. Its SI unit is m/s².
• G is the Universal Gravitational Constant, which is a scalar quantity and remains the same throughout the universe. Its value is approximately 6.674 x 10^-11 N m²/kg².
• Weight vs. Mass:
• Mass is the amount of matter in an object and remains constant regardless of location.
• Weight (W = mg) is the force with which an object is attracted towards the center of the Earth. Since g varies, the weight of an object changes depending on its position in the universe.
• Gravity on the Moon:
• The mass and radius of the Moon are smaller than those of the Earth. Consequently, the acceleration due to gravity on the Moon is about 1/6^th of that on Earth (approx. 1.62 m/s²).

Important Points

• Variation with Shape: Because the Earth is flattened at the poles and bulged at the equator, the equatorial radius is about 21 km longer than the polar radius. Since g is inversely proportional to the square of the radius, it is stronger at the poles.
• Variation with Altitude: As one moves away from the surface of the Earth, the distance from the center of gravity increases, causing the value of g to decrease.
• Variation with Depth: When moving towards the center of the Earth, the effective mass of the Earth attracting the object decreases. At the center of the Earth, the value of g becomes zero.
• Variation due to Rotation: The rotation of the Earth creates a centrifugal force that acts outwards, effectively reducing the value of g, most significantly at the equator.

The correct answer is Better adaptability and chances of survival.

Key Points

• Variation refers to the morphological, physiological, and behavioral differences among individuals belonging to the same species.
• It ensures better adaptability because environments are never static; they undergo constant changes such as climate shifts, resource scarcity, or the emergence of new predators.
• Individuals possessing favorable variations are more likely to survive and reproduce in a specific environment, a process central to Charles Darwin’s theory of Natural Selection.
• If all individuals in a population were genetically identical, a single adverse change (like a lethal disease or temperature rise) could potentially wipe out the entire population.
• Variation acts as a buffer, ensuring that at least some individuals have the traits necessary to endure environmental stress, thereby preventing extinction.

Additional Information

• Sources of Variation:
• Genetic Recombination: Occurs during meiosis through crossing over, resulting in new combinations of alleles in offspring.
• Mutation: A sudden, stable change in the DNA sequence. While some mutations are harmful, others introduce beneficial traits that drive evolution.
• Sexual Reproduction: The fusion of gametes from two different parents ensures genetic diversity.
• Types of Variation:
• Continuous Variation: Traits that show a range of phenotypes, such as human height or skin color.
• Discontinuous Variation: Traits that fall into distinct categories, such as blood groups (A, B, AB, O) or the ability to roll one's tongue.
• Importance in Evolution:
• Variation is the raw material for evolution. Over millions of years, the accumulation of small variations can lead to speciation (the formation of new species).
• It allows organisms to exploit different ecological niches and adapt to diverse geographic locations.
• Analysis of Other Options:
• No mutations: Variation is actually fueled by mutations; without them, the genetic pool would remain stagnant.
• No evolution: Variation is the fundamental requirement for evolution; without it, evolution would cease.
• Similar response: Variation ensures individuals respond differently to environmental changes, allowing the fittest to survive.

Important Points

• The survivability of an individual depends on whether its variations are adaptive or non-adaptive for its specific habitat.
• In asexual reproduction, variation is minimal and usually occurs only due to DNA copying errors or mutations.
• In sexual reproduction, variation is much higher, which is why sexually reproducing organisms generally show greater resilience to environmental fluctuations.
• The study of how variations are passed from one generation to the next is known as Genetics, a field pioneered by Gregor Mendel in the 19^th century.

The correct answer is Both (i) and (iii).

Key Points

• Work Done is defined as the product of the component of the force in the direction of the displacement and the magnitude of this displacement. Mathematically, it is expressed as W = Fs cosθ, where θ is the angle between the force vector and the displacement vector.
• Statement (i): The work done by a force can indeed be negative. This occurs when the force acts in a direction opposite to the displacement (i.e., the angle θ is 180° or obtuse). A classic example is the work done by friction on a sliding body, which is always negative because friction opposes motion. ***Hence, statement

(i) is incorrect.***

• Statement (ii): When the force and displacement are in the same direction, the angle θ is 0°. Since cos 0° = 1, the work done is positive and reaches its maximum value (W = Fs). ***Hence, statement

(ii) is correct.***

• Statement (iii): The S.I. unit of work done is the Joule (J), which is equivalent to 1 Newton-meter (N·m). Pascal (Pa) is the S.I. unit for pressure or stress, defined as one Newton per square meter. ***Hence, statement

(iii) is incorrect.***

• Since the question asks for statements that are NOT true, both (i) and (iii) fit the criteria. Hence, the correct answer is Both (i) and (iii).

Additional Information

• Nature of Work:
• Work is a scalar quantity, meaning it has only magnitude and no direction, even though both force and displacement are vector quantities.
• The dimensional formula for work is [ML²T⁻²], which is identical to the dimensions of energy and torque.
• Zero Work Conditions:
• Work done is zero if the displacement is zero (e.g., pushing against a rigid wall).
• Work is zero if the force is zero.
• Work is zero if the force is perpendicular to the displacement (θ = 90°). For example, the centripetal force acting on a satellite in a circular orbit does zero work because it is always perpendicular to the velocity.
• Units of Work:
• In the CGS system, the unit of work is the erg.
• The relationship between the S.I. and CGS units is 1 Joule = 10⁷ ergs.
• Other units include Kilowatt-hour (kWh), often used for electrical energy, where 1 kWh = 3.6 × 10⁶ Joules.

Important Points

• Work-Energy Theorem: It states that the net work done by all forces acting on a body is equal to the change in its kinetic energy. This is a fundamental principle in classical mechanics.
• Types of Work:
• Positive Work: Angle θ is acute (0° ≤ θ < 90°). Example: Lifting an object (work done by the lifting force).
• Negative Work: Angle θ is obtuse (90° < θ ≤ 180°). Example: Work done by gravitational force when an object is moved upwards.
• Zero Work: Angle θ is 90°. Example: A person carrying a suitcase horizontally (the upward lifting force is perpendicular to the horizontal displacement).
• Constant vs. Variable Force: While the question specifies a constant force, work done by a variable force is calculated using integration of the force over the path of displacement.

The correct answer is Focal length of a convex lens is taken as negative..

Key Points

• For spherical lenses, we follow the New Cartesian Sign Convention, where the optical centre (O) of the lens is taken as the origin and the principal axis is taken as the X-axis.
• According to this convention, the object is always placed to the left of the lens. This implies that the light from the object falls on the lens from the left-hand side. Hence, statement 1 is correct.
• The focal length of a concave lens is considered negative because its principal focus lies on the left side of the optical centre, opposite to the direction of incident light. Hence, statement 2 is correct.
• All distances measured to the right of the origin (along the positive x-axis) are taken as positive, while those measured to the left are taken as negative. Hence, statement 3 is correct.
• A convex lens is a converging lens, and its principal focus is located on the right side of the lens. Therefore, according to the sign convention, the focal length of a convex lens is always positive, not negative. Hence, statement 4 is incorrect.
• Therefore, the statement "Focal length of a convex lens is taken as negative" is NOT correct.

Additional Information

• Lens Formula: The relationship between the object distance (u), image distance (v), and focal length (f) is given by the formula 1/v - 1/u = 1/f. In this formula, u is always negative for a real object.
• Magnification (m): It is the ratio of the height of the image to the height of the object. For lenses, m = h'/h = v/u. A positive magnification indicates a virtual and erect image, while a negative magnification indicates a real and inverted image.
• Power of a Lens (P): The degree of convergence or divergence of light rays achieved by a lens is expressed as its power. It is the reciprocal of the focal length in metres (P = 1/f). The SI unit of power is Dioptre (D).
• Sign of Power: Since the focal length of a convex lens is positive, its power is also positive. Conversely, since the focal length of a concave lens is negative, its power is negative.

Important Points

• Height Measurement: Distances measured perpendicularly above the principal axis (along the +y-axis) are taken as positive, which is usually the case for the height of the object.
• Inverted Images: Distances measured perpendicularly below the principal axis (along the -y-axis) are taken as negative. This applies to the height of real images.
• Incident Light Direction: The convention is designed such that distances measured in the direction of incident light are positive, and those measured against the direction of incident light are negative.
• Optical Centre: Every measurement for spherical lenses must originate from the optical centre, unlike mirrors where measurements start from the pole.

The correct answer is ribosomes; lipids.

• The Endoplasmic Reticulum (ER) is a large network of membrane-bound tubes and sheets that stretches from the nuclear envelope to the plasma membrane.
• Rough Endoplasmic Reticulum (RER) looks rough under a microscope because it has particles called ribosomes attached to its surface.
• These ribosomes are the primary sites of protein synthesis in the cell. The proteins manufactured here are then sent to various places in the cell depending on the need.
• Smooth Endoplasmic Reticulum (SER) does not have ribosomes attached to its surface, giving it a smooth appearance.
• The SER plays a crucial role in the synthesis of lipids (fats) and steroid hormones, which are essential for cell function and the building of the cell membrane.
• Therefore, the correct association is that RER bears ribosomes for protein synthesis, while SER synthesizes lipids. Hence, the correct answer is ribosomes; lipids.
• Functions of Smooth Endoplasmic Reticulum (SER):
• In the liver cells of vertebrates, SER plays a vital role in detoxifying many poisons and drugs.
• It is also involved in the metabolism of carbohydrates and the storage of calcium ions, which is particularly important in muscle cells (where it is called the sarcoplasmic reticulum) for muscle contraction.
• Functions of Rough Endoplasmic Reticulum (RER):
• Apart from protein synthesis, the RER is involved in protein folding and quality control, ensuring that only correctly folded proteins proceed to the Golgi apparatus.
• It provides a large surface area for chemical reactions and serves as a pathway for the distribution of materials.
• Membrane Biogenesis:
• Some of the proteins and lipids synthesized by the ER help in building the cell membrane. This process is known as membrane biogenesis.
• Other proteins and lipids function as enzymes and hormones throughout the biological system.
• Structural Components:
• The ER membrane is similar in structure to the plasma membrane and consists of a lipid bilayer.
• It exists in three forms: cisternae (flattened sacs), vesicles, and tubules. RER is mainly composed of cisternae, while SER is mainly composed of tubules.
• Ribosomes:
• These are small, dense, granular structures found either freely in the cytoplasm or attached to the RER. They are composed of Ribosomal RNA (rRNA) and proteins and are known as the "protein factories" of the cell.

The correct answer is Heat is used to break the bonds between molecules.

Key Points

• When ice is heated, its temperature rises until it reaches its melting point, which is 0°C (273.15 K) under standard atmospheric pressure.
• Once the ice starts to melt, the heat energy supplied is no longer used to increase the kinetic energy of the water molecules. Instead, it is used to overcome the intermolecular forces of attraction (specifically hydrogen bonds) that hold the water molecules in a solid crystalline structure. Hence, the statement that heat is used to break bonds is correct.
• Since the average kinetic energy of the molecules remains unchanged during this process, the thermometer shows no rise in temperature until all the ice has completely converted into liquid water.
• This absorbed energy, which does not result in a temperature change, is called the Latent Heat of Fusion. The word latent means "hidden," as this heat is hidden from the temperature scale.
• The statement that ice absorbs heat but does not melt is scientifically incorrect because, at the melting point, the absorption of heat directly causes the phase change from solid to liquid.
• The statement that ice reflects heat is incorrect in this context; while ice has a high albedo (reflectivity), the question specifically addresses what happens to the heat that is absorbed by the ice.
• The statement that ice becomes denser is a physical fact (water is denser than ice), but it is a result of the molecular bonds breaking, not the reason why the temperature remains constant.

Additional Information

• Latent Heat of Fusion: For water, the latent heat of fusion is approximately 334 Joules per gram (or 80 calories per gram). This is the amount of energy required to change 1 gram of ice at 0°C to 1 gram of water at 0°C.
• Phase Change: During a phase change, the system exists in a state of thermal equilibrium where two phases (solid and liquid) coexist. The temperature will only begin to rise again once the phase transition is 100% complete.
• Specific Heat Capacity: Once the ice has completely melted into water, the heat supplied will then increase the temperature of the water based on its specific heat capacity, which is 4.184 J/g°C.
• Molecular Structure: Ice has a unique hexagonal lattice structure. When heat breaks these molecular bonds, the molecules actually move closer together in the liquid state, which is why water is more dense than ice.

Important Points

• Kinetic vs. Potential Energy: In thermodynamics, temperature is directly proportional to average kinetic energy. During melting, the heat increases the potential energy of the molecules (by changing their position and breaking bonds) rather than their speed.
• Effect of Pressure: The melting point of ice can be lowered by increasing the external pressure. This phenomenon is known as regelation, which allows ice to melt under pressure and refreeze once the pressure is removed.
• Latent Heat of Vaporization: A similar process occurs when water boils at 100°C. The temperature remains constant because the heat is used as Latent Heat of Vaporization to turn liquid water into steam.
• Numerical Value: The Latent Heat of Fusion of water is significantly higher than many other substances, which helps in regulating the Earth's climate by slowing the melting of polar ice caps.

The correct answer is It becomes n times larger than for a single turn.

Key Points

• The magnetic field strength produced by a current-carrying circular coil at its center is directly proportional to the number of turns (n) in the coil.
• When a circular coil has n turns, the current flows in the same direction in every turn, which means the magnetic field produced by each individual turn adds up vectorially.
• For a single turn, the magnetic field is produced by the current flowing through that one loop; for n turns, the fields of all n loops are superposed, resulting in a field that is n times as strong.
• If the current (I) is kept constant, the total magnetic field (B) is given by the product of n and the field of a single loop. Hence, the statement that it becomes n times larger is correct.
• This linear relationship assumes that the turns are tightly wound and the radius of the coil remains significantly unchanged for each turn.

Additional Information

• Mathematical Formula: The magnetic field (B) at the center of a circular coil of radius (r) carrying current (I) with n turns is expressed as B = (μ₀ * n * I) / (2 * r), where μ₀ is the permeability of free space (approximately 4π × 10⁻⁷ T·m/A).
• Magnetic Field and Current: The strength of the magnetic field is directly proportional to the magnitude of the current. If the current is doubled, the magnetic field also doubles, provided other factors remain constant.
• Inversely Proportional to Radius: The magnetic field strength is inversely proportional to the radius of the circular coil. A smaller radius results in a stronger field at the center because the current-carrying wire is closer to the center point.
• Direction of the Field: The direction of the magnetic field produced by a circular loop can be determined using the Right-Hand Thumb Rule. If the fingers of the right hand curl in the direction of the current, the thumb points in the direction of the magnetic field.
• SI Unit: The SI unit of magnetic field strength or magnetic flux density is the Tesla (T). In smaller applications, the unit Gauss (G) is also used, where 1 Tesla = 10,000 Gauss.
• Applications: This principle is used in the construction of solenoids, electromagnets, electric motors, and galvanometers, where increasing the number of turns is a common method to amplify magnetic force without increasing the current.

Important Points

• Biot-Savart Law: This fundamental law in electromagnetism describes how a magnetic field is generated by a steady electric current. It is the basis for calculating the field produced by circular coils.
• Ampere’s Circuital Law: Another crucial law used to find the magnetic field for highly symmetric current distributions, such as an infinitely long wire or a toroid.
• Superposition Principle: The fact that the field becomes n times larger is an application of the superposition principle, which states that the total magnetic field at any point is the vector sum of the individual fields produced by each segment of the current.

The correct answer is Double displacement.

Key Points

• A Neutralisation reaction is a fundamental chemical process where an acid and a base react with each other to produce salt and water.
• It is categorized as a Double displacement reaction (also known as a metathesis reaction) because the cations and anions of the two reacting compounds exchange partners to form new products.
• In a typical aqueous neutralisation, the Hydrogen ions (H+) from the acid combine with the Hydroxide ions (OH-) from the base to form H2O (water).
• A standard example of this reaction is HCl (Hydrochloric acid) reacting with NaOH (Sodium hydroxide) to form NaCl (Sodium chloride) and H2O. In this case, the Sodium (Na+) and Hydrogen (H+) ions effectively swap places.
• These reactions are usually exothermic in nature, meaning they involve the release of heat energy during the formation of water.

Additional Information

• Single displacement reaction:
• In this type of reaction, a more reactive element displaces a less reactive element from its compound.
• For example, when Zinc (Zn) is added to Copper sulfate (CuSO4), it displaces the copper to form Zinc sulfate (ZnSO4) and Copper (Cu). Hence, statement 1 is incorrect.
• Combustion reaction:
• This is a high-temperature redox reaction between a fuel and an oxidant (usually atmospheric Oxygen).
• It results in the release of energy in the form of light and heat, often producing Carbon dioxide (CO2) and Water as byproducts when hydrocarbons are burned. Hence, statement 2 is incorrect.
• Decomposition reaction:
• This occurs when a single reactant breaks down into two or more simpler products.
• This process often requires energy in the form of heat, light, or electricity. An example is the heating of Calcium carbonate (CaCO3) to yield Calcium oxide (CaO) and Carbon dioxide (CO2). Hence, statement 3 is incorrect.
• Double displacement reaction:
• This reaction involves the exchange of ions between two compounds to form two new compounds.
• The general chemical equation is AB + CD → AD + CB. Since a neutralisation reaction involves the H+ from the acid and OH- from the base swapping to form water, while the remaining ions form a salt, it is a classic Double displacement. Hence, statement 4 is correct.

Important Points

• pH Levels: The pH of the resulting solution in a neutralisation reaction depends on the strength of the reactants. A reaction between a strong acid and a strong base results in a neutral salt with a pH of 7.
• Applications: Neutralisation is widely used in agriculture to treat acidic soil using slaked lime (Calcium hydroxide), and in medicine where Antacids (bases) are used to neutralise excess gastric acid in the stomach.
• Titration: In analytical chemistry, neutralisation reactions are the basis of acid-base titrations, which are used to determine the unknown concentration of an acidic or basic solution using an indicator.

The correct answer is Atoms get added to unsaturated bonds.

Key Points

• An addition reaction is a fundamental class of chemical reactions where two or more molecules combine to form a larger single molecule. This typically occurs in organic compounds containing multiple bonds.
• In this process, atoms or groups of atoms are added across the unsaturated bonds (double or triple bonds) of a molecule, such as alkenes or alkynes. Hence, statement 3 is correct.
• During an addition reaction, the pi (π) bond of the unsaturated system is broken, and two new sigma (σ) bonds are formed. This results in the conversion of an unsaturated hydrocarbon into a saturated one.
• Functional groups being replaced by others is the characteristic of a substitution reaction, which is common in saturated hydrocarbons like alkanes. Hence, statement 1 is incorrect.
• The removal of atoms from a molecule to form a double or triple bond is known as an elimination reaction, which is essentially the reverse of an addition reaction. Hence, statement 2 is incorrect.
• While oxidation involves the loss of electrons or increase in oxidation state, an addition reaction specifically focuses on the structural incorporation of new atoms into the molecular framework through covalent bonding. Hence, statement 4 is incorrect.

Additional Information

• Types of Addition Reactions:
• Electrophilic Addition: Commonly seen in alkenes and alkynes, where an electrophile attacks the electron-rich double bond. A classic example is the halogenation of ethene.
• Nucleophilic Addition: Typical of compounds containing carbon-heteroatom multiple bonds, such as carbonyl groups (aldehydes and ketones), where a nucleophile attacks the electron-deficient carbon atom.
• Free Radical Addition: Occurs in the presence of peroxides or UV light, often following a non-Markovnikov pathway.
• Hydrogenation:
• This is a specific type of addition reaction where hydrogen gas (H2) is added to unsaturated compounds in the presence of a catalyst like Nickel (Ni), Palladium (Pd), or Platinum (Pt).
• Industrial use: It is widely used in the food industry to convert vegetable oils (unsaturated fats) into vanaspati ghee (saturated fats).
• Bromine Water Test:
• Addition reactions are used as a diagnostic tool to detect unsaturation. When bromine water (reddish-brown) is added to an unsaturated compound, an addition reaction occurs, and the solution becomes colorless.
• Markovnikov's Rule:
• In the addition of a protic acid (like HBr) to an asymmetric alkene, the hydrogen atom attaches to the carbon with the greater number of hydrogen atoms, while the halide group attaches to the carbon with more alkyl substituents.

Important Points

• Hybridization Change: In an addition reaction involving an alkene, the hybridization of the carbon atoms changes from sp2 to sp3 as the geometry shifts from planar to tetrahedral.
• Saturated vs Unsaturated: Saturated compounds contain only single bonds and are generally less reactive, whereas unsaturated compounds contain double (C=C) or triple (C≡C) bonds, making them highly susceptible to addition.
• Atom Economy: Addition reactions are considered highly efficient in green chemistry because they have a 100% atom economy; all atoms in the reactants are present in the final product, leaving no waste or byproducts.
• Polymerization: Addition polymerization is a critical industrial process where thousands of monomer molecules (like ethylene) undergo repeated addition reactions to form polymers (like polyethylene).

The correct answer is presence of excess air.

Key Points

• The process of converting sulphide ores into oxides by heating them strongly in the presence of excess air is known as Roasting.
• Metals that lie in the middle of the activity series, such as Zinc (Zn), Iron (Fe), and Lead (Pb), are often found in nature as sulphides or carbonates.
• It is much easier to obtain a metal from its oxide than from its sulphide; therefore, the sulphide ore must be oxidized before reduction can occur.
• A classic example of Roasting is the treatment of Zinc Blende (ZnS). When heated in excess air, it reacts to form Zinc Oxide (ZnO) and releases Sulphur Dioxide (SO2) gas. The chemical equation is: 2ZnS + 3O2 → 2ZnO + 2SO2.
• In this process, Oxygen acts as the oxidizing agent to remove the Sulphur impurities in the form of volatile gas. Hence, the condition of excess air is correct.

Additional Information

• Calcination: Unlike roasting, Calcination is the process used for carbonate ores. It involves heating the ore strongly in the absence of oxygen or a limited supply of air to expel carbon dioxide. For example, ZnCO3 (Calamine) is heated to produce ZnO and CO2.
• Reactivity Series: The metals in the middle of the series (like Zn, Fe, Pb) are moderately reactive. Metals at the top (like Na, Ca, Mg) are extracted by electrolysis, while metals at the bottom (like Au, Ag) are often found in a native state.
• Reduction: Once the ore is converted to a metal oxide, it is reduced to the free metal using a reducing agent like Carbon (Coke). This is a crucial step in pyrometallurgy.
• Sulphur Dioxide Management: The SO2 gas produced during the Roasting of sulphide ores is a major air pollutant but is often collected and used in the Contact Process to manufacture Sulphuric Acid (H2SO4).

Important Points

• Temperature Control: During Roasting, the temperature must be maintained below the melting point of the metal or the ore to prevent the mass from fusing together, which would hinder the oxidation process.
• Removal of Volatile Impurities: Apart from converting sulphides to oxides, Roasting also helps in removing moisture and organic matter, as well as volatile impurities like Arsenic and Antimony in the form of their oxides.
• Specific Ores: Common sulphide ores subjected to roasting include Galena (PbS) for Lead, Copper Pyrites (CuFeS2) for Copper, and Cinnabar (HgS) for Mercury.
• Chemical Nature: Roasting is an exothermic process because the oxidation of metal sulphides releases a significant amount of thermal energy, which helps maintain the high temperature required for the reaction.