Mathematics and Science PYQs

Nurturing creativity in students involves creating an environment where they feel free to explore, experiment, and think independently.

 Key Points

• Encouraging creativity requires emphasizing tasks that promote critical thinking, problem-solving, and innovative approaches rather than focusing solely on correct answers or rigid evaluations.
• Engaging students in inquiry and discovery-oriented tasks is essential for fostering creativity. These tasks encourage exploration, questioning, and learning through discovery, which are key aspects of creative thinking.
• Encouraging students to do tasks without any fear of evaluation is also important. When students are not afraid of making mistakes or being judged, they are more likely to take risks, explore new ideas, and approach problems in creative ways.

Hint

• Highlighting right or wrong responses (B) and encouraging students to always find the right answers to textbook questions (D) can stifle creativity.
• It focuses on conformity and correctness, rather than allowing room for exploration and innovative thinking.

Hence, the correct answer is (A) and (C).

The nature of science involves understanding that it is not only about individual achievements but also about collective efforts, ongoing change, and interaction with different fields of knowledge. 

Key Points

• The statement "several others before him worked on it but failed" reflects the idea that science is a collective enterprise.
• Scientific advancements often result from the work of many individuals, building on each other's ideas and efforts, even if they don't always succeed in the first attempt.
• The statement also indicates that science is dynamic (B), as scientific knowledge and technological inventions evolve over time. What was once unsuccessful can become successful as new ideas, techniques, and tools emerge.

Hint

• Science being interdisciplinary (A) could be relevant in some contexts, but it isn't directly indicated by the teacher's remark about Edison.
• Science promoting skepticism (D) is not directly illustrated here, as the teacher is acknowledging previous work rather than questioning it.

Hence, the correct answer is (B) and (C).

Scientific modeling is a tool used by scientists to represent and understand complex systems or phenomena. Models are simplified representations of real-world systems that help scientists test hypotheses, predict behaviors, and analyze various factors in a controlled and manageable way.

Key Points

• The correct reason why scientists use scientific modeling is that models are simpler to analyze than real systems.
• Real-world systems are often very complex, involving many variables and interactions that are difficult to study directly.
• By creating models, scientists can focus on the most important aspects of a system, making it easier to analyze and predict its behavior.

Hint

• Models can test hypotheses by simulating different conditions and outcomes, which is one of the main purposes of scientific modeling.
• Modeling often requires instruments (e.g., computers, sensors) for creating, simulating, and analyzing models.
• Modeling usually involves calculations and may require computational tools to simulate scenarios accurately.

Hence, the correct answer is models are simpler to analyze than real system.

CONCEPT:

Observation vs. Inference

• In science, an observation is a direct statement about what is seen or measured, based on sensory perception or instrumentation, without interpretation.
• An inference, on the other hand, is a conclusion drawn from observations or evidence. It is based on reasoning and extends beyond the immediate data to make an assumption or explanation.
• In the given

Statements:

• S1 ("Oxygen is a supporter of combustion") is an inference because it is a conclusion drawn from experiments where oxygen helps sustain combustion but doesn’t directly combust itself.
• S2 ("Oxygen is a non-combustible gas") is also an inference because it’s based on the observation that oxygen itself does not combust but supports combustion.

EXPLANATION:

• Statement S1 ("Oxygen is a supporter of combustion") is an inference because it is based on the observed fact that oxygen enables combustion, but it does not directly react (combust) itself.
• Statement S2 ("Oxygen is a non-combustible gas") is an inference because it’s concluded from the observation that oxygen does not undergo combustion in the typical sense, though it is required for combustion reactions to occur.
• Both statements are based on experimental observation, but they are conclusions (inferences) drawn from those observations, rather than direct sensory measurements or descriptions.

Thus, the correct answer is: S1 - Inference; S2 - Inference

This involves fluid pressure and air pressure in a closed container. Water flows out of a hole when the pressure inside the liquid exceeds the external pressure. If the container is sealed, the trapped air can influence whether water flows or not.

Key Points

• Here, the girl seals the bottle with a cap and covers the hole with her thumb.
• When she removes her thumb, the air trapped above the water prevents free flow because the pressure inside the bottle becomes less than the atmospheric pressure outside.
• Since the outside pressure is higher than the pressure at the hole, water will not spurt out.

Hence**, the water will not spurt out of the hole because the pressure inside the bottle is less than the outside pressure.**

CONCEPT:

Properties and Uses of Bakelite and PVC

• Bakelite is a type of thermosetting plastic, which means it undergoes an irreversible chemical change when heated, forming a hard, durable material.
• It is commonly used to make electrical insulators, utensil handles, and other heat-resistant products because of its excellent insulating properties and hardness after molding.
• PVC (Polyvinyl Chloride) is a thermoplastic, meaning it becomes soft and moldable when heated, and it can be remolded multiple times.
• PVC is used to make containers, pipes, electrical insulation, and other products requiring flexibility, strength, and chemical resistance.

EXPLANATION:

• Bakelite, being a thermosetting plastic, is used in making electrical switches and utensil handles due to its heat resistance and durability.
• PVC, as a thermoplastic, is widely used for making containers due to its flexibility and moldability, and it is also used for electrical insulation because of its ability to provide protective covering in wiring.
• Therefore, the correct answers are:
• A – thermosetting plastic; B – electrical switches;
• C – thermoplastic; D – containers.

Thus, the correct answer is: A - thermosetting plastic; B - electrical switches; C - thermoplastic; D - containers

CONCEPT:

Oxides, Water, and Oxygen Reactions

• When an oxide reacts with water, it forms either an acidic or a basic solution depending on what type of oxide it is.
• If an oxide is from a non-metal, it usually forms an acidic solution when it reacts with water. If it’s from a metal, it typically forms a basic solution.
• When a substance reacts with oxygen, it can form either an acidic or a basic product, depending on the nature of the original substance.
• If something turns blue litmus paper red, that means it’s acidic.

EXPLANATION:

• An oxide of substance X reacts with water to form Y. Since Y turns blue litmus paper red, Y is acidic.
• Next, Y reacts with oxygen to form Z. Since Y is acidic, Z is also likely to be acidic when it reacts with oxygen.
• Since Y is acidic and turns blue litmus red, X must be a non-metal, because non-metal oxides are usually acidic.

Therefore, the correct answer is: X is a non-metal, Y is acidic, and Z is acidic in nature.

CONCEPT:

Displacement Reaction

• A displacement reaction occurs when a more reactive element displaces a less reactive element from a compound.
• Chlorine (Cl₂) is more reactive than bromine (Br₂), so chlorine can displace bromine from sodium bromide (NaBr) to form sodium chloride (NaCl) and bromine gas (Br₂).
• This is an example of a halogen displacement reaction, where chlorine displaces bromine from sodium bromide.

EXPLANATION:

The reaction is as follows:

Cl₂(g) + 2NaBr(aq) → 2NaCl(aq) + Br₂(g)

• When chlorine gas (Cl₂) is added to a solution of sodium bromide (NaBr), chlorine being a stronger oxidizing agent displaces bromine from sodium bromide.
• This reaction leads to the formation of sodium chloride (NaCl) and bromine gas (Br₂), as chlorine replaces bromine in the ionic bond.

Therefore, the correct answer is: Sodium chloride is formed through displacement reaction.

Key Points

Burning of candle: 

• A candle flame is divided into three zones.
• The temperatures in each zone are varied.
• Each zone has a distinctive colour, which will aid us in determining the temperatures in each zone.

The innermost zone 

• The color of flame here is dark black.
• It basically pertains to the unburnt wax vapors.
• This region is the least hot region.

The middle zone 

• The color of the flame is yellow.
• This zone is bright and luminous.
• The wax vapors here are burnt partially.
• The partially burnt fuel in this zone releases carbon particles.
• These carbon parties are responsible for the smoke and the soot being released into the air.
• The temperature of this zone is moderate.

The outermost zone

• The color of this zone is blue.
• This is the region where complete combustion is taking place.
• It is the hottest part of the region.
• It is the non-luminous part of the flame.

EXPLANATION:

• Statement 1 is true: The yellow part of the flame is indeed the region of partial combustion, where carbon particles are heated but not completely burned.
• Statement 2 is true: The innermost zone does not support burning and contains unburnt wax vapours. This part of the flame is cooler.
• Statement 3 is true: The non-luminous part of the flame is the zone of complete combustion, where oxygen reacts with the wax vapours to produce carbon dioxide and water vapor, and the flame is blue and hot.
• Statement 4 is not true: The temperature of the middle zone (yellow, luminous part) is not the same as the temperature of the non-luminous part of the flame. The non-luminous part is hotter than the middle zone due to the complete combustion occurring in the outermost zone.

Thus, the statement that is not true is: The temperature of middle zone and the non-luminous part of the flame is same.

CONCEPT:

Thermos Flask and Heat Insulation

• A thermos flask is designed to minimize the heat exchange between the contents and the external environment. It typically consists of two layers: an inner layer and an outer layer, with a medium between them.
• The key function of the medium between the two layers is to prevent the loss of heat through conduction, convection, and radiation.
• To prevent heat loss through conduction and convection, the medium used between the inner and outer layers of the flask should ideally be a vacuum. This is because a vacuum has no air molecules, which are the carriers of heat transfer by conduction and convection.
• In addition, the outer layer of the thermos flask is usually coated with a reflective material (often silvered) to minimize heat loss through radiation.

EXPLANATION:

• The medium between the inner and outer layers of a thermos flask is a vacuum. This is because a vacuum prevents heat loss due to conduction (since there are no molecules to transfer heat) and convection (since there is no air to move and carry heat away).

Thus, the correct answer is: Vacuum, because it prevents loss of heat due to conduction and convection.

CONCEPT:

Purification of Copper using Electrolysis

• The purification of copper is typically done using the process of electrolysis, where impure copper is used as the anode, pure copper is deposited at the cathode, and the electrolyte is a copper salt solution, usually copper sulfate (CuSO₄).
• The electrolysis process helps to purify the copper by dissolving copper from the impure anode and depositing pure copper at the cathode, while the impurities (such as metals like iron, silver, and gold) either stay in the solution or fall to the bottom as anode mud.

EXPLANATION:

• Option 1: The correct setup involves using impure copper as the anode, pure copper as the cathode, and a copper sulfate solution as the electrolyte. This allows copper to dissolve from the anode and deposit as pure copper at the cathode. This is the standard method for copper purification.
• Option 2: This option is incorrect because pure copper cannot be used as the anode in the purification process. The anode needs to be impure copper, as it is the source of the copper that is dissolved and deposited at the cathode.
• Option 3: This option is incorrect because water alone does not provide the necessary copper ions for the purification process. Copper sulfate solution is required to allow copper to dissolve and be deposited at the cathode.
• Option 4: This option is incorrect because carbon is typically used as an anode in some electrolysis processes, but not in copper purification. The anode should be impure copper in this case, and copper sulfate is the correct solution for electrolysis.

Thus, the correct answer is: Anode - Impure copper; Cathode - Pure copper; Solution - Copper sulfate

Calculation:

When a ray of light enters two media X and Y with different optical densities, the following changes occur:

Change in speed of light:

When the light passes from a less dense medium to a denser medium, the speed of light decreases. Therefore, the change in speed of light in medium X will be an increase, and in medium Y, it will decrease.

Change in frequency of light:

The frequency of light does not change when light passes from one medium to another. This is because the frequency is determined by the source of the light, not by the medium. Hence, for both media X and Y, the frequency remains the same (A = No change).

Change in wavelength of light:

The wavelength of light depends on both the speed of light and the frequency. Since the frequency remains constant and the speed changes, the wavelength must also change. If the speed increases (medium X), the wavelength increases, and if the speed decreases (medium Y), the wavelength decreases. Therefore, for X, the wavelength increases (B), and for Y, the wavelength decreases (D).

Correct Answer: Option 1: A—No change; B— Increases; C-Decreases; D—No change

Calculation:

The process by which dead vegetation is converted to fossil fuel under high pressure and temperature is known as carbonization. The correct terms for filling in the blanks are:

A: The type of fossil fuel formed from dead vegetation is coal, as coal is formed by the carbonization of plant material.

B: The pressure is high during the formation of coal because high pressure leads to the conversion of organic material into coal over time.

C: The temperature is also high in the process of carbonization, which is necessary to break down the organic material and form coal.

D: The process of converting dead vegetation into coal is called carbonization because it involves the conversion of plant material into carbon-rich substances like coal.

Correct Answer: Option 2: A-coal; B-high; C-high; D-carbonization

CONCEPT:

pH and pH Indicators

• pH is a measure of how acidic or basic a substance is. A pH value less than 7 indicates an acidic substance, while a pH value greater than 7 indicates a basic substance. A pH value of 7 is neutral.
• pH indicators, such as pH paper, are used to determine the acidity or alkalinity of a solution. Different colors on the pH paper correspond to different pH values.
• Yellowish-orange on pH paper typically indicates a weakly acidic solution, with a pH around 4-6.

EXPLANATION:

• 1) Vinegar: Vinegar is acidic with a pH around 2-3, which would turn the pH paper red, not yellowish-orange. Therefore, this is not the correct answer.
• 2) Common salt: Common salt (NaCl) is neutral and does not affect the pH of a solution. It would not cause any color change on pH paper, so this is not the correct answer.
• 3) Milk of magnesia: Milk of magnesia is a basic substance with a pH of around 10-11. It would turn the pH paper blue or green, indicating an alkaline solution.
• 4) Lemon juice: Lemon juice is acidic with a pH around 2-3, which would turn the pH paper red, not yellowish-orange. Thus, this is not the correct answer either.

The correct answer is Milk of magnesia.

Calculation:

For making a fuse wire, the following properties are required:

Resistance: The fuse wire should have high resistance so that it heats up quickly and melts when the current exceeds a certain limit.

Thickness: The wire should be thin so that it can melt easily when the current becomes high.

Melting point: The wire should have a low melting point so that it melts quickly under excessive current.

The correct choice for making a fuse wire is Option 4: High resistance, Thin thickness, Low melting point.

The correct answer is (D)  → (A) → (B) → (C)

Explanation:

• Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into usable forms for plants and other organisms.
• The nitrogen cycle involves several steps that transform nitrogen into various compounds and incorporate it into living organisms.
• (D) Fixation of nitrogen from atmosphere by certain bacteria and blue-green algae: This is the initial step in the nitrogen cycle. Certain bacteria and blue-green algae (cyanobacteria) convert atmospheric nitrogen (N₂) into ammonia (NH₃) or related forms, which can be further processed into other nitrogenous compounds.
• (A) Uptake of compounds of nitrogen by plants through the root system: Plants absorb these nitrogenous compounds, such as nitrates and ammonium, through their roots from the soil. This step is crucial for the incorporation of nitrogen into the plant's system.
• (B) Synthesis of plant proteins and other compounds: Once inside the plant, the absorbed nitrogen is used to synthesize plant proteins, nucleic acids, and other vital compounds necessary for growth and development.
• (C) Conversion of nitrogenous wastes from dead plants and animals into nitrogenous compounds: After nitrogen has been fixed, it is further converted into different forms within the soil. Decomposing bacteria and other microorganisms break down nitrogenous wastes from dead plants and animals into ammonia and other compounds, which can be used by plants.

Explanation:-

• Month C: Temperature = 27°C, Wind speed = 0.71 m/s, Humidity = 75.50%
• Month D: Temperature = 26°C, Wind speed = 0.82 m/s, Humidity = 75.22%
• Month A: Temperature = 26°C, Wind speed = 0.87 m/s, Humidity = 83.12%
• Month B: Temperature = 29°C, Wind speed = 2.91 m/s, Humidity = 72.33%

Conclusion: Month B has the highest temperature (29°C) and the highest wind speed (2.91 m/s), even though it has slightly lower humidity. These factors suggest that the highest evaporation rate will occur in Month B.

Correct Answer: Option 4 - Month B

The correct answer is Seedlings are formed after pollination and development of embryo

Explanation:

• Sexual reproduction in flowering plants involves the process of pollination, fertilization, embryo formation, and ultimately, the growth of seedlings.
• The sequence of events in sexual reproduction starts with the transfer of pollen grains from the anther to the stigma (pollination), followed by the fertilization of the ovule, development of the embryo, and finally the formation of seedlings.
• Pollination: The transfer of pollen grains from the male part (anther) of a flower to the female part (stigma).
• Fertilization: After successful pollination, the pollen grain germinates on the stigma and grows a pollen tube that carries the sperm cells to the ovule. Fertilization occurs when one of the sperm cells fuses with the egg cell in the ovule, forming a zygote.
• Development of embryo: The zygote develops into an embryo inside the seed. This embryo will eventually grow into a new plant.
• Formation of seedlings: Once the embryo has matured and seeds are dispersed, under suitable conditions, the seed germinates, and seedlings are formed. These seedlings grow into mature plants.

Based on this sequence, the correct statement is that seedlings are formed after pollination and development of embryo.

The correct answer is Endocrine glands secrete hormones through ducts.

Explanation:

Endocrine glands are ductless glands that secrete hormones directly into the bloodstream or surrounding tissues. These hormones regulate various physiological processes such as growth, metabolism, and reproduction.

• Pituitary gland is attached to the brain: This statement is true. The pituitary gland is located at the base of the brain and is connected to the hypothalamus.
• Endocrine glands secrete hormones: This statement is true. Endocrine glands produce and release hormones that have specific effects on target organs.
• Pancreas and adrenals are endocrine glands: This statement is true. The pancreas and adrenal glands are part of the endocrine system. The pancreas secretes insulin and glucagon, and the adrenal glands produce corticosteroids and catecholamines.
• Endocrine glands secrete hormones through ducts: This statement is not true. Endocrine glands are characterized by their lack of ducts and secrete hormones directly into the bloodstream.

The correct answer is Both (A) and (R) are true and (R) is the correct reasoning for (A).

Concept:

• Deforestation is the removal of trees and forests, often to make way for agricultural activities or urban development.
• Infiltration rate: The rate at which water penetrates into the soil. Trees and vegetation increase the infiltration rate by allowing water to percolate into the ground through their roots.

Explanation:

• Assertion (A): Deforestation can lead to floods: This statement is true. Deforestation results in the removal of trees that help in retaining and absorbing water, leading to an increased risk of floods during heavy rainfall.
• Reasoning (R): The infiltration rate of water is reduced due to deforestation: This statement is also true. When trees are removed, the soil's ability to absorb water decreases, leading to quicker runoff and reduced groundwater recharge. As a result, more water flows on the surface, which can contribute to flooding.

Conclusion:

Both the assertion and the reasoning are true, and the reduced infiltration rate due to deforestation is a correct explanation for why deforestation can lead to floods.