Key Concept: Scientific Questioning

c) It compares two distinct conditions and is testable
[Solution Description]
A good scientific question is testable, specific, and leads to further investigation. The given question meets these criteria because:
1) It compares two clear conditions (fresh vs. stored dough).
2) It can be tested through experimentation by controlling other variables.
3) The outcome (puffing behavior) is observable and measurable.
This type of question encourages systematic investigation and deeper understanding.

Key Concept: Data Interpretation, Scientific Reasoning

b) Three consistent trials with controlled variables showing the same trend
[Solution Description]
Reliable scientific conclusions require consistent, repeatable results with proper controls. Multiple trials showing similar patterns with controlled variables provide the strongest evidence.
Step 1: Conduct minimum 3 trials per temperature to check consistency.
Step 2: Ensure identical dough composition and thickness for all tests.
Step 3: Verify trend holds across trials (e.g., always faster at higher temps).
Step 4: Check no other variables changed between tests.
Step 5: Statistical analysis showing significant difference strengthens conclusion.

Key Concept: Experimental Design

a) Size of the rolled dough
[Solution Description]
According to the syllabus, when investigating how oil temperature affects puri puffing, other factors like dough thickness and dropping method should remain constant for valid results.

Key Concept: Scientific Observation, Hypothesis Formation

b) Steam is seen escaping when the phulka puffs up
[Solution Description]
Scientific hypotheses must be based on observable phenomena and lead to testable predictions. The observation that steam forms inside should be prioritized as it suggests a physical mechanism (water vaporization) that can be experimentally verified.
Step 1: Observe steam escaping from puffed phulka indicates water turning to vapor.
Step 2: Recognize this suggests heat causes water in dough to evaporate.
Step 3: Formulate hypothesis: "Steam pressure from vaporizing water causes swelling."
Step 4: This leads to testable predictions like pricking holes should prevent puffing.

Key Concept: Scientific Investigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that changing only one variable while keeping others constant ensures reliable results, which is true because it minimizes confounding factors. The Reason correctly explains why this is important—it isolates the effect of the independent variable. Therefore, both statements are true, and the Reason justifies the Assertion.

Key Concept: Curiosity, Observation, Scientific Inquiry

d) It motivates asking questions and exploring unknown aspects of observations.
[Solution Description]
Curiosity drives the student to question a common observation, prompting deeper investigation into the underlying principles of heat transfer and material expansion. This initial wonder leads to forming hypotheses and conducting experiments, exemplifying how curiosity fuels scientific inquiry.

Key Concept: The Importance of Curiosity in Science

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that scientific investigations often start with simple observations and questions related to everyday occurrences. This is true because many scientific discoveries have originated from such observations. The reason mentions that questions like why a puri puffs up when fried stimulate curiosity, which is fundamental to scientific inquiry. This is also true since curiosity drives scientists to explore and understand natural phenomena. Moreover, the reason correctly explains the assertion because curiosity, triggered by such questions, leads to systematic investigation, forming the basis of science.

Key Concept: Scientific Investigation Process

d) To test hypotheses systematically and improve understanding.
[Solution Description]
The syllabus highlights that scientific investigations involve moving beyond simple observations to structured experiments that test hypotheses. Experiments help refine understanding through careful data collection and analysis, rather than just confirming biases or memorizing facts.

Key Concept: Role of Observation & Creativity

c) Balancing careful observation with creative thinking.
[Solution Description]
The syllabus emphasizes balancing **careful observation** (rigorous data gathering) with **creative thinking** (exploring new ideas). This combination ensures reliable yet innovative scientific progress, unlike approaches that prioritize only one aspect.

Key Concept: Scientific Wonder, Hypothesis Formation

d) The role of imaginative questioning in understanding natural phenomena.
[Solution Description]
This question highlights how scientific wonder involves comparing seemingly unrelated large-scale phenomena to understand magnitudes and scales in nature. It encourages abstract thinking and estimation, which are critical for developing hypotheses and models in science.

Key Concept: Scientific Investigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that changing only one variable at a time in an experiment ensures accurate results, which is correct as per scientific methodology. The reason provided explains why this is necessary: keeping other variables constant helps isolate and identify the specific effect of the changed variable. This explanation correctly justifies the assertion. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Observation and Measurement

b) To compare results under different conditions
[Solution Description]
Measuring the time taken for a puri to puff up provides quantitative data that can help in understanding how different factors (like oil temperature or dough thickness) affect the puffing process. This measurement allows for objective analysis and comparison between different experimental conditions.

Key Concept: Variables in Experimentation

c) Whether the puri puffs up or not.
[Solution Description]
Dependent variables are the outcomes that are measured in an experiment. In the puri experiment, whether the puri puffs up (yes/no), time taken to puff up, and thickness of the puffed side are dependent variables because they depend on changes made to independent variables like oil temperature or dough thickness.

Key Concept: Scientific Questions

d) It should be focused, testable, and based on measurable observations.
[Solution Description]
A scientific question must be testable, measurable, and based on observable phenomena. For the puri example, it should focus on variables that can be controlled and measured, such as thickness, oil temperature, or dough composition. The question should lead to hypotheses that can be tested through experiments.

Key Concept: Scientific Question Formation, Systematic Investigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that the given question about oil temperature and puri puffing is scientifically valid because it follows the principle of changing one variable (temperature) while controlling others. This aligns with the Reason, which explains that focused scientific questions enable systematic investigation through variable isolation. Both statements are true, and the Reason correctly justifies the Assertion since controlled experiments form the basis of scientific inquiry.

Key Concept: Designing Experiments

c) Angle of the ramp
[Solution Description] The independent variable is the factor that is deliberately changed in an experiment. Here, the angle of the ramp is manipulated to observe its effect on the speed of the ball. Therefore, the angle of the ramp is the independent variable.

Key Concept: Scientific Investigation

b) Plants grown under white light
[Solution Description] The control group provides a baseline for comparison and should be exposed to natural white light (or no special treatment) to ensure that any observed effects are solely due to the experimental conditions (blue or red light).

Key Concept: Controlled Experiments, Variables

c) The time taken for sugar to dissolve completely
[Solution Description]
The dependent variable is what is measured in response to changes in the independent variable (stirring rate). Here, the time taken for sugar to dissolve depends on how fast the solution is stirred.

Key Concept: Making Observations

b) Increased molecular motion due to heat
[Solution Description] The rate at which a solute (sugar) dissolves in a solvent (water) increases with temperature because higher temperatures provide more energy to break the bonds between solute particles and allow them to mix more freely with the solvent molecules.

Key Concept: Scientific Inquiry, Variables in Experiments

b) Whether the puri puffs up or not
[Solution Description]
In a scientific experiment, the dependent variable is what you measure or observe as the outcome. For the puri puffing experiment, the dependent variable is whether the puri puffs up (yes/no) or the time it takes to puff up (seconds). The thickness of the dough or type of flour are independent variables that can be changed to observe their effect on the dependent variable.

Key Concept: Scientific Investigation Steps

c) To identify the effect of one variable and ensure reliable results
[Solution Description]
In scientific investigations, changing only one variable at a time helps in isolating the effect of that specific variable on the outcome. If multiple variables are changed simultaneously, it becomes difficult to determine which variable caused the observed change. This approach ensures accurate and reliable results.

Key Concept: Systematic Investigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In systematic investigation, it is important to change only one variable at a time while keeping all other conditions the same. This approach helps in accurately determining the effect of the specific variable being tested. The assertion states that changing one variable ensures accurate results, which is true because isolating variables reduces ambiguity in observations. The reason provided explains why this practice is followed—by keeping other conditions constant, we can clearly attribute any observed changes to the altered variable. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Observation in Science

c) Sensory details like smell, sound, and visual changes
[Solution Description]
During a scientific investigation, meticulous recording of sensory observations such as smell, sound, visual changes (e.g., puffing), oil splatter, and temperature changes is crucial. These details help in analyzing the results and forming conclusions.

Key Concept: Scientific Inquiry, Observation and Experimentation

c) To isolate the effect of each variable
[Solution Description]
Changing only one variable at a time helps in identifying the exact cause of the observed effect. If multiple variables are changed simultaneously, it becomes difficult to determine which variable caused the change in the outcome.

Key Concept: Observation, Hypothesis Formation

c) Vary the moisture content of the dough and observe swelling behavior
[Solution Description]
To test the hypothesis that steam causes the swelling, the experiment must manipulate moisture content. One approach is to prepare dough with varying moisture levels (e.g., dry, normal, and extra moist) and observe if swelling changes. Another method is to measure the internal temperature of the phulka during cooking to confirm steam formation. The key is ensuring only moisture content varies while keeping other conditions consistent.

Key Concept: Experimental Design

d) All of the above except thickness variation
[Solution Description]
To isolate the effect of dough thickness on puri puffing, variables like oil temperature, type of flour, and method of dropping the dough must remain constant. Changing only one factor at a time ensures accurate observations.

Key Concept: Scientific Inquiry

d) Assuming the reason without testing
[Solution Description]
Systematic investigation involves controlled experiments, careful observation, and recording data. Jumping to conclusions without experimentation or ignoring observations contradicts scientific methods.

Key Concept: Scientific Observation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that changing only one variable at a time ensures reliable results, which is correct because it aligns with the principle of controlled experiments mentioned in the syllabus. The Reason explains that this isolates the effect of the specific variable, which is also true and directly justifies the Assertion. Thus, both are true, and the Reason correctly explains the Assertion.

Key Concept: Observation, Experimentation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that high oil temperature can cause puris to burn instead of puffing uniformly. This is true because excessive heat leads to rapid evaporation of water from the dough, which disrupts the even puffing process. The reason explains that rapid water evaporation causes localized overheating, which is scientifically accurate and directly supports the assertion. Thus, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Controlled Experiments

c) To isolate the effect of that variable
[Solution Description]
In a controlled experiment, changing only one variable at a time helps to isolate its effect on the dependent variable while keeping other factors constant. This ensures that any observed changes are due to the manipulated variable alone.

Key Concept: Hypothesis and Controlled Variables

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that increasing oil temperature speeds up puffing due to higher energy transfer, which aligns with the principle that heat accelerates cooking processes. The Reason correctly explains that controlling other variables ensures only temperature affects the result. Since both statements are true and the Reason logically justifies the Assertion, the correct choice is option (a).

Key Concept: Scientific Questions and Observations

a) Curiosity and careful observation
[Solution Description]
Science begins with curiosity and careful observation of everyday phenomena.

Key Concept: Systematic Investigation

b) Record them systematically
[Solution Description]
Observations made during an experiment should be recorded systematically to analyze the results accurately. This step is crucial for drawing valid conclusions.

Key Concept: Observation and Questioning

c) Observing the phenomenon
[Solution Description]
The scientific process starts with careful observation and questioning. Before conducting experiments or forming hypotheses, one must first observe the phenomenon and ask relevant questions about it. Observing that puris puff up when fried is the foundational step.

Key Concept: Scientific Inquiry, Experiment Design

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that maintaining constant dough thickness while varying oil temperature isolates the effect of oil temperature on puri puffing. This is correct because controlling other variables ensures that only the independent variable (oil temperature) affects the outcome. The reason explains why controlling variables is important - to establish a clear cause-effect relationship by eliminating confounding factors. Since both the assertion and reason are true, and the reason correctly explains the assertion, the correct answer is option a).

Key Concept: Designing Experiments

d) All of the above
[Solution Description]
To ensure valid results in an experiment studying the effect of sunlight on plant growth, all variables except sunlight exposure should be kept constant (controlled). This includes factors like water amount, soil type, and temperature. Changing only one variable (sunlight) while keeping others constant helps isolate its effect.

Key Concept: Scientific process, Iterative investigation

c) Investigate whether pricking holes in the dough affects puffing differently at various thicknesses
[Solution Description]
The scientific method is iterative. After drawing initial conclusions, good scientists develop new questions to deepen understanding. Testing alternative explanations helps validate findings, while simply repeating identical experiments has diminishing returns. Publishing immediately would be premature without further validation.

Key Concept: Key Principles of Scientific Investigation

b) To ensure results are consistent and not due to chance
[Solution Description]
Repeatability ensures that experiment results are consistent and reliable when reproduced under the same conditions by other scientists. It validates findings and eliminates bias or errors unique to a single trial.

Key Concept: Scientific Observation

b) They might lead to new scientific questions
[Solution Description]
The syllabus states that unexpected observations may lead to new questions. Detailed recording helps refine understanding and guides further investigation, which is fundamental to scientific inquiry.

Key Concept: Variables in Experiment

c) Thickness of the rolled dough
[Solution Description]
A controllable variable is something that the experimenter can change intentionally. From the syllabus, examples include the thickness of the dough, type of flour, temperature of oil, or method of dropping the dough into the oil.

Key Concept: Scientific Investigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that controlling one variable at a time is essential in scientific investigation, which is true as per the syllabus which mentions "Changing one variable at a time while keeping others constant". The reason given is that changing multiple variables makes it difficult to determine causation, which is also true and directly explains why controlling one variable is important. Therefore both are true and reason correctly explains the assertion.

Key Concept: Scientific Investigation Steps

b) Ask a scientific question
[Solution Description]
The first step in scientific investigation is to ask a scientific question based on observations. According to the syllabus, it involves identifying what you want to explore, such as why a puri puffs up when fried or how different variables affect this process.

Key Concept: Variables in Experimentation

b) Thickness of the rolled dough
[Solution Description]
A controlled variable is something kept constant during the experiment to ensure that only one factor is tested at a time. From the syllabus, examples include the thickness of the rolled dough or type of flour used. The temperature of the oil is not a controlled variable if it is being changed to test its effect.

Key Concept: Investigating Variables

a) Temperature of the hot oil
[Solution Description]
A controlled variable is what we intentionally change during an experiment while keeping other factors constant. In the puri puffing experiment, examples include the thickness of the dough, type of flour, oil temperature, and method of dropping the dough.

Key Concept: Oil Temperature Impact

c) Moderate temperature allows one side to become thinner while puffing
[Solution Description]
The temperature of the oil determines how quickly water in the dough turns to steam. If the oil is too cold, the dough absorbs oil without puffing. If too hot, it burns before proper puffing. Optimal temperature causes quick steam formation, leading to puffing with one side thinner as steam escapes unevenly.

Key Concept: Scientific Question

b) How does oil temperature affect puffing time?
[Solution Description]
Scientific questions focus on testable variables like those listed in the syllabus—thickness of dough, oil temperature, or method of dropping the dough. A valid question should aim to explore cause-and-effect relationships.

Key Concept: Phenomenon of Puri Puffing, Heat Transfer

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that the thinner side of the puri puffs up more due to lower thermal resistance and faster steam escape. This is true as thinner dough offers less resistance to heat transfer, allowing steam to form and expand faster. The Reason explains that the thinner side heats up quicker because of reduced thickness, leading to rapid vaporization of water and expansion of trapped air, which is scientifically accurate. Additionally, the Reason correctly explains the Assertion by detailing the mechanism behind the phenomenon—reduced thickness accelerates heating and steam formation, causing the puffing effect.

Key Concept: Experiment Design

c) Oil temperature
[Solution Description]
In an experiment where dough thickness is the independent variable, other factors like oil temperature, type of flour, and method of dropping the dough must be kept constant to isolate the effect of dough thickness alone on the puffing outcome.

Key Concept: Identifying Variables

b) Dough thickness, oil temperature, and dropping method.
[Solution Description]
To isolate the effect of flour type, other variables like dough thickness, oil temperature, and method of dropping must remain unchanged. This ensures that any differences observed are due to flour type alone.

Key Concept: Controlling Variables

b) The puri puffs up more quickly but may burn.
[Solution Description]
Increasing the oil temperature causes the water in the dough to evaporate faster, creating steam that makes the puri puff up more quickly. However, if the oil is too hot, the puri may brown too fast or even burn before it puffs properly.

Key Concept: Measuring Changes

c) The upward-facing side expands more, becoming thinner.
[Solution Description]
When the puri is placed in hot oil, steam forms inside the dough, causing it to puff. The side facing upwards expands more due to direct exposure to heat, making it thinner compared to the lower side, which remains slightly thicker.

Key Concept: Hypothesis Formation

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The Assertion states that the hypothesis about uneven steam escape can be tested by rolling dough uniformly. This is true because varying thickness is an independent variable, and observing puffing tests the hypothesis. The Reason explains the purpose of controlled experiments, which is valid. However, the Reason does not directly explain why rolling dough uniformly tests the hypothesis; it instead provides a general principle of experimentation. Thus, both are true, but the Reason does not correctly explain the Assertion.

Key Concept: Hypothesis Formation

c) A possible explanation based on observations that can be tested
[Solution Description]
A hypothesis is a possible explanation based on observations, which can be tested through experiments. For example, "A puri puffs up because steam forms inside the dough." It is not just a guess but an educated assumption backed by initial observations.

Key Concept: Analyzing Results

d) Revise the hypothesis and retest with new experiments
[Solution Description]
If the experiment's results do not match the hypothesis, you should revise the hypothesis based on the new evidence and conduct further tests. Science involves refining ideas through experimentation.

Key Concept: Heat transfer

b) Oil temperature
[Solution Description]
The rate of heat transfer $Q = mc\Delta T$ depends on mass (m), specific heat capacity (c), and temperature difference $\Delta T$. Among the given options, oil temperature directly affects $\Delta T$, which is the driving force for heat transfer.

Key Concept: Identifying Variables

d) Oil temperature
[Solution Description]
The independent variable is the factor that is deliberately changed in the experiment to observe its effect. Here, oil temperature is the factor being varied to study its impact on puri puffing.

Key Concept: Experimental Error and Reproducibility

b) Not maintaining the same oil temperature for each trial
[Solution Description]
Inconsistent results often arise due to uncontrolled variables. Here, not maintaining the exact oil temperature across trials would lead to variation in puffing times. Other options (measuring device, hypothesis, or flour type) are less likely if they were kept constant as required. Thus, option b) is correct.

Key Concept: Controlled Experiments, Analyzing Results

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion claims that thinner dough always yields better results based on faster puffing time (quantitative) despite uneven puffing (qualitative). This is incorrect because scientific conclusions must consider both quantitative and qualitative data for validity. The reason states that quantitative data alone is sufficient, which is false because qualitative observations (e.g., unevenness) provide critical context. Thus, the assertion is false due to incomplete analysis, and the reason is false because both data types are essential.

Key Concept: Dependent Variable

c) Size of the fried puri
[Solution Description]
The dependent variable is what you measure or observe as the outcome of the experiment. Here, the size (diameter) of the puri is measured after frying, so it is the dependent variable.

Key Concept: Observing Outcomes

c) Time taken for the puri to puff up
[Solution Description]
Observable or measurable outcomes are the results that are tracked during an experiment to analyze the effect of changes made to controlled variables. Examples include whether a puri puffs up, time taken to puff up, and final shape and texture.

Key Concept: Identifying Variables

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The temperature of the hot oil is listed as a controlled variable in the syllabus, meaning it can be adjusted during the experiment. The reason correctly defines controlled variables as those that can be changed, which aligns with the assertion.

Key Concept:  Identifying variables: what can be controlled and observed

(c) Dough thickness and oil temperature
[Solution Description]
In this experiment, the aim is to study how the type of flour affects the puffing of puris. Here, the type of flour is the independent variable because it is changed during the experiment. The observed variable is the puffing of the puri, such as puffing height, puffing time, or amount of puffing. Dough thickness and oil temperature should be kept the same for all puris so that the experiment remains fair. Therefore, they are controlled variables, not observed variables.

Key Concept: Controlled Experiment

c) To clearly identify the effect of the changed variable
[Solution Description]
Changing only one variable at a time ensures that any observed effect on the outcome can be attributed solely to that variable. If multiple variables are changed, it becomes unclear which factor caused the change in the result.

Key Concept: Measurement Tools and Techniques

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The Assertion states that a ruler is used to measure the length of an object accurately, which is true because rulers are standard tools for length measurement. The Reason provided is that rulers have standardized markings that allow for precise length measurements, which is also true and correctly explains why rulers are accurate for measuring lengths. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Scientific Investigation

c) To keep all conditions the same except for one variable being tested
[Solution Description]
A controlled experiment ensures that only one variable is changed at a time while keeping all other conditions constant. This helps in accurately determining the effect of the independent variable on the dependent variable.

Key Concept: Experimental Variables, Systematic Investigation

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that recording only whether the puri puffs up is sufficient for analyzing the effect of oil temperature. However, this is incorrect because scientific experiments require multiple measurements to establish a reliable relationship. For example, measuring the time taken to puff can indicate how quickly the reaction occurs at different temperatures, while thickness measurement can show variations in the degree of puffing with temperature changes.
The Reason claims that these additional measurements provide no further insight, which is false. In reality, they are crucial for comprehensive analysis. Hence, the Assertion is false, and the Reason is also false.

Key Concept: Data Collection, Qualitative vs Quantitative Observations

b) As a categorical variable describing splatter intensity (low/medium/high)
[Solution Description]
Scientific observations can be qualitative (descriptive) or quantitative (numerical). Since "more splattering" is a relative description without exact measurement, it should be recorded as a qualitative observation using standardized descriptors (e.g., low/medium/high splattering) alongside quantitative data like oil temperature. This provides comprehensive evidence for analysis.

Key Concept: Identifying Variables

b) To keep all conditions the same except for one factor being tested
[Solution Description]
Changing only one variable at a time helps isolate its effect on the outcome. This ensures that any change observed is due to that specific variable and not influenced by others.

Key Concept: Recording Observations in Experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that keeping detailed records of experimental steps and observations is important for scientific research, which is true. The reason given is that accurate records help ensure experiments can be repeated by other scientists, which is also true and directly explains why keeping records is important. Therefore, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Recording Data

c) They provide additional data that may reveal new patterns or problems
[Solution Description]
Unexpected observations can lead to new insights or questions, helping refine the scientific understanding and design of future experiments.

Key Concept: Experimental Design

b) To ensure the results are not influenced by external factors
[Solution Description]
Changing only one independent variable at a time ensures that any observed effect on the dependent variable can be attributed solely to that change. If multiple variables are altered simultaneously, it becomes difficult to determine which variable caused the observed effect.

Key Concept: Observation and Measurement

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Observation and measurement are fundamental in science. The assertion states that accurate measurement is essential for valid conclusions, which is true because precise data allows reliable analysis. The reason explains that measurements provide quantitative data for identifying patterns, which is also true and directly supports the assertion. Thus, both are true, and the reason correctly explains the assertion.

Key Concept: Systematic Investigation

b) Thickness of dough
[Solution Description]
According to the principle of systematic investigation, only one variable (oil temperature) should be changed while keeping all other conditions (like thickness of dough, type of flour, and method of dropping dough) constant to isolate its effect.

Key Concept: Observation and Measurement

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that accurate measurement of oil temperature is essential for determining the puffing time of puris, which is true because temperature plays a crucial role in cooking processes. The reason explains that temperature affects the rate at which moisture turns to steam, leading to puffing, which is also scientifically correct. Furthermore, the reason logically explains why the assertion is true—higher temperatures cause faster steam formation, reducing puffing time, while lower temperatures do the opposite. Hence, both statements are true, and the reason correctly explains the assertion.

Key Concept: Tools, Qualitative vs. Quantitative Observation

d) The puri puffed up quickly
[Solution Description]
Qualitative observations describe qualities or characteristics without using numbers. "The puri puffed up quickly" is descriptive and lacks numerical data, making it qualitative. The other options are quantitative as they include measurable quantities.

Key Concept: Systematic investigation

c) To identify which variable causes the observed effect
[Solution Description]
Changing only one variable at a time ensures that any observed effect can be directly attributed to that specific variable. If multiple variables are changed simultaneously, it becomes difficult to determine which variable caused the observed change.
The correct answer highlights this principle: "To identify which variable causes the observed effect."

Key Concept: Observation, Controlled Experiment

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that changing the thickness of the dough affects the puffing time of a puri due to altered heat transfer rate, which aligns with the principle of systematic investigation where varying one parameter (thickness) impacts the observable outcome (puffing time). The Reason correctly explains that heat transfer rate is inversely proportional to thickness, meaning thicker dough leads to slower heat transfer and longer puffing time. Both statements are conceptually correct, and the Reason directly justifies the Assertion.

Key Concept: Observing changes and responses in experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that keeping the thickness of the dough constant while varying the oil temperature is an example of controlling variables. This is true because in scientific experiments, controlled variables are the factors that remain unchanged to ensure that any observed effects are due to the independent variable (oil temperature). The reason explains what controlled variables are, which aligns with the assertion and correctly justifies it. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Systematic observation, Variable control

b) Thickness of dough, oil temperature, type of flour, and dropping method
[Solution Description]
For a valid experiment, all other variables must be controlled (kept constant) except the one being tested (hole-pricking). This includes thickness of dough, oil temperature, type of flour, and method of dropping the dough.

Key Concept: Effect of Temperature on Puffing

a) Oil is too cold
[Solution Description]
The puffing of a puri depends on the temperature of the oil. If the oil is not hot enough, the water inside the dough does not turn to steam quickly, preventing the puri from puffing. The ideal frying temperature for puris is around 180°C to 200°C, as this ensures rapid steam formation and even cooking. Thus, insufficient oil temperature leads to no puffing.

Key Concept: Time Measurement, Observation

a) Higher oil temperature reduces puffing time
[Solution Description]
Higher oil temperature increases the rate of steam generation in the dough, reducing puffing time. Here, $180^\circ \mathrm{C}$ oil causes faster puffing (8 s) compared to $150^\circ \mathrm{C}$ This inverse relationship between temperature and time is correctly stated in option a).

Key Concept: Measurement, Variables, Systematic Investigation

c) Prepare puris with varying thickness but identical oil temperature and flour
[Solution Description]
A valid scientific approach involves changing only one variable (here, dough thickness) while keeping others (oil temperature, flour type, dropping method) constant. Observations must include measurable outcomes like puffing time or thickness of the thinner side. Option c) follows this systematic method.

Key Concept: Controlling Variables

d) All of the above
[Solution Description]
When studying the effect of dough thickness on puri puffing, other variables like oil temperature, type of flour, and method of dropping the dough must be kept constant. Changing multiple variables simultaneously can make it unclear which factor caused the observed result. Consistency in these parameters ensures the experiment isolates the impact of dough thickness alone.

Key Concept: Systematic Observation

c) To analyze results systematically and draw reliable conclusions
[Solution Description] Detailed notes help in understanding the experiment better, identifying patterns, refining experiments, and uncovering new insights. They ensure reliability and accuracy in scientific investigations.

Key Concept: Analyzing Results

b) Comparing different variables (e.g., thickness, temperature) to see how they affect puffing
[Solution Description]
Analyzing results involves comparing the recorded data to identify trends or correlations. For example, plotting graphs of puffing time ($t$) vs. dough thickness ($d$ mm) can reveal whether thicker dough takes longer to puff. This method helps draw meaningful conclusions.

Key Concept: Systematic Investigation

d) Altering one variable at a time while controlling other factors
[Solution Description]
To systematically investigate why puris puff up, a scientist should conduct controlled experiments by altering one variable at a time while keeping others constant. For instance, they can test how thickness or size of the dough affects puffing while maintaining consistent frying temperature and oil quality.

Key Concept: Observation, Control Variables, Data Analysis

c) Uncontrolled dough thickness makes it hard to attribute changes in puffing solely to oil temperature.
[Solution Description]
The experiment's results will be unreliable because not controlling dough thickness introduces an additional variable. Since both oil temperature and dough thickness can affect puffing, it becomes impossible to isolate the effect of oil temperature alone. Systematic errors may arise, leading to incorrect conclusions.

Key Concept: Real-World Application

d) Making careful observations and systematic experiments
[Solution Description]
Careful observation and systematic experimentation are key steps in scientific investigations. They help form hypotheses, test them under controlled conditions, and draw conclusions about everyday phenomena such as puri puffing up.

Key Concept: Variables in Scientific Inquiry

b) Type of flour used for the dough
[Solution Description]
A controlled variable is a factor that remains constant during an experiment to ensure that any changes observed are due to the manipulated variable only. In the context of frying a puri, controlled variables include factors like thickness and size of the dough, type of flour, and method of dropping the dough into the oil.

Key Concept: Observational Outcomes

b) Whether the puri puffs up (yes/no)
[Solution Description]
Observable outcomes in an experiment are measurable or describable results. For frying a puri, these include whether it puffs up, the time taken to puff up, and the thickness of its sides.

Key Concept: Experimental Design

c) To ensure clarity in identifying the cause of observed changes
[Solution Description]
Changing only one variable at a time allows us to clearly identify its direct impact on the result. If multiple variables are altered simultaneously, it becomes difficult to pinpoint which variable caused any observed changes, leading to inconclusive results.

Key Concept: Electricity and Technology

b) Using the heating effect of electric current
[Solution Description]
Electricity produces heat through the heating effect of electric current, which is utilized in devices like heaters and electric blankets to provide warmth during cold weather.

Key Concept: Understanding Forces and Pressure

b) Because of the gravitational pull of the Earth
[Solution Description]
A ball thrown upward falls back due to the force of gravity acting downward. Gravity is a fundamental force that attracts objects towards the center of the Earth, causing them to return to the ground after being projected upward.

Key Concept: Force and Pressure, Pressure Differences

c) As a result of lower atmospheric pressure at higher altitudes
[Solution Description]
The boiling point of water decreases with a decrease in atmospheric pressure. At higher altitudes, the atmospheric pressure is lower because there is less air above pushing down. This reduced pressure lowers the boiling point of water. In contrast, at the coastal town, the atmospheric pressure is higher due to more air above, resulting in a higher boiling point for water. Therefore, water boils at a lower temperature in the city.

Key Concept: Health and Medicine

c) To boost immunity against specific diseases
[Solution Description]
Vaccines are developed using scientific methods to protect individuals from infectious diseases by stimulating the immune system to recognize and combat pathogens without causing the disease itself.

Key Concept: Particles and States of Matter

c) Particles in solids vibrate but cannot move freely, while gas particles move freely due to weaker forces and larger spaces.
[Solution Description]
In solids, particles are tightly packed in a fixed arrangement, held by strong intermolecular forces, restricting their movement to small vibrations. In gases, particles are far apart with weak intermolecular forces, allowing them to move freely and rapidly in all directions.

Key Concept: Material Behavior, Heat Transfer

c) Time taken decreases
[Solution Description]
The puffing of puri occurs due to the rapid formation of steam inside when water evaporates. Higher oil temperature increases the rate of heat transfer to the puri, causing faster evaporation and reduced time for puffing.
Step 1: Heat transfer rate ($Q$) is directly proportional to the temperature difference between oil and puri ($\Delta T$).
Step 2: Increasing $\Delta T$ by 20°C accelerates heat transfer.
Step 3: Faster heat transfer means quicker formation of steam, reducing the puffing time.
Thus, the time taken decreases as oil temperature increases.

Key Concept: Phases of the Moon

c) Less sunlight reflects off the Moon as it orbits
[Solution Description]
After a full moon, the Moon's illuminated portion decreases as it moves in its orbit around Earth. This makes the Moon appear smaller (waning phase) until it reaches a new moon. The change is due to the relative positions of the Sun, Earth, and Moon.

Key Concept: Reflection and Light

c) Light converges to a focal point after passing through a convex lens.
[Solution Description]
A convex lens is thicker in the middle and thinner at the edges. When parallel rays of light pass through it, they converge at a focal point on the other side due to refraction. This bending occurs because light slows down as it enters the denser lens material, causing the rays to change direction toward the normal and then diverge again after exiting.

Key Concept: Investigating everyday phenomena

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Both Assertion and Reason are true. Steam forms inside the puri when heated because the water content in the dough turns into vapor. This steam creates pressure inside the dough, causing it to expand (puff up). Therefore, the Reason correctly explains why the Assertion occurs.