Key Concept: Scientific Investigation, Experimental Design

c) Systematically varying one factor while keeping others constant
[Solution Description]
A good scientific investigation requires systematic testing of variables while controlling others. The best approach would be to methodically test each potential factor (dough thickness, oil temperature, etc.) independently while keeping other conditions constant, recording observations carefully to identify causal relationships.
Step 1: Identify all possible factors that might affect puri puffing (thickness, oil temp, flour type, dropping method).
Step 2: Design experiments where only one variable is changed at a time.
Step 3: Maintain consistent observation methods for all trials.
Step 4: Record quantitative data where possible (e.g., puffing time).
Step 5: Compare results systematically to draw conclusions.

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: Scientific Investigation

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that observations lead to questions, which is true as scientific investigations begin with curiosity-driven questions based on initial observations. The reason explains how observations are made using senses, which is also true. However, the reason does not directly explain why observations lead to questioning; it merely describes the process of observation. Thus, both are true but the reason is not the correct explanation.

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

c) How you feel about cooking
[SolutionDescription]
While smell, puff time and oil splatter are relevant observations mentioned in the syllabus, personal feelings aren't part of scientific recording.

Key Concept: Observation, Experimental Approach

d) The phenomenon involves complex interactions not yet fully understood.
[Solution Description]
Even simple observations like the swelling of a puri involve complex interactions of heat, moisture, and material properties that are not yet fully modeled. This demonstrates how science continuously evolves as new methods and theories develop to explain everyday phenomena.

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: Curiosity in Science

d) It drives questioning, observation, and deeper exploration of natural phenomena.
[Solution Description]
Curiosity motivates scientists to ask "Why?" and "How?" questions about natural phenomena, leading to observations, hypotheses, and experiments. The syllabus explicitly states that science begins with wonder and simple questions, which evolves into structured investigations. Thus, curiosity is essential for initiating scientific inquiry.

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: Nature of Scientific Inquiry

b) To show how science starts with simple observations
[Solution Description]
The text uses the puri example to show how everyday observations can lead to scientific questions. It explains this demonstrates systematic investigation and notes scientists still don't fully understand this phenomenon.

Key Concept: Scientific Investigation, Controlled Experiments

c) Preparing puris with different thicknesses but using the same oil type, temperature, and frying time
[Solution Description]
A controlled experiment requires changing only one variable (dough thickness) while keeping all other conditions (oil type, oil temperature, frying duration) constant. Option c) describes an experiment where dough thickness varies, but all other factors remain unchanged, ensuring that any observed differences in puffing are due to dough thickness alone.

Key Concept: Scientific Question Characteristics

c) Why does a puri puff up when fried in hot oil?
[Solution Description]
A focused scientific question is clear, specific, and can be investigated through experiments or observations. It should not be too broad or vague. Among the given options, "Why does a puri puff up when fried in hot oil?" is a focused scientific question as it targets a specific phenomenon and can be tested experimentally.

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: 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: Systematic Investigation

b) It ensures that the results are due to the specific variable being tested.
[Solution Description]
Changing only one variable at a time ensures that any observed effect can be attributed specifically to that variable. If multiple variables are changed simultaneously, it becomes difficult to determine which variable caused the observed outcome. This principle is fundamental to maintaining control and validity in experiments.

Key Concept: Variables in Experiments

c) Type of flour used
[Solution Description]
A controlled variable is one that is kept constant during the experiment. In studying puri puffing, factors like type of flour and oil temperature are examples of controlled variables when changed intentionally between trials.

Key Concept: Observation Skills

c) Unexpected observations
[Solution Description]
Good scientific documentation includes recording all experimental conditions, measurements, and any unexpected observations made during the investigation.

Key Concept: Variables, Controlled Experiments

a) Keeping the oil temperature constant throughout the experiment
[Solution Description]
The student must control all other variables that could affect the puffiness of puris, such as the oil temperature and dough thickness, while only changing the amount of baking soda. This ensures that any observed changes in puffiness are solely due to the variation in baking soda.

Key Concept: Scientific Questions, Observations

c) Recording the height of plants daily using a ruler
[Solution Description]
Quantitative data involves measurable numerical values. Measuring the height of plants daily provides specific, repeatable data that can be analyzed statistically, unlike qualitative descriptions like "healthy" or "green."

Key Concept: Variables in Experiments

d) To isolate the effect of the changed variable
[Solution Description]
Changing only one variable at a time ensures that any observed effect can be attributed solely to that variable. This helps in identifying cause-and-effect relationships accurately.

Key Concept: Scientific Inquiry, Controlled Experiments

a) Size of the rolled dough
[Solution Description]
To study the effect of oil temperature (independent variable), all other factors like dough thickness, type of flour, and method of dropping the dough must be kept constant. This ensures that any change in puffing is only due to the oil temperature and not other variables.

Key Concept: Variables in Experiments

d) The temperature of the oil
[Solution Description]
In a scientific experiment about puri puffing, variables that can be tested include dough thickness, oil temperature, type of flour, or pricking holes in the puri before frying. These variables directly influence the puffing behavior and can be systematically tested.

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: 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: Scientific Observation

d) Moisture evaporates faster from one side, making it thinner
[Solution Description]
The thickness difference in a puri occurs due to the way steam gets trapped inside the dough during frying. When the dough is dropped into hot oil, moisture turns into steam and expands, causing the puri to puff up. One side becomes thinner because steam escapes more easily from that side, creating uneven expansion.

Key Concept: Types of Observations

c) The puri took 30 seconds to puff up
[Solution Description]
Quantitative observations involve numerical measurements, such as counting or using instruments to obtain measurable data, unlike qualitative observations which describe characteristics without numbers.

Key Concept: Controlled Experiment

c) To ensure the effect is due to the changed variable alone
[Solution Description]
Changing only one variable at a time ensures that any observed effects can be directly attributed to that specific variable, avoiding confusion caused by multiple changes influencing the outcome.

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: 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: Scientific Questions and Observations

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

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: 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: Experimental Design, Variables

b) Whether the puri puffs up or not
[Solution Description]
The dependent variable is what is measured or observed in response to changing the independent variable (flour type). Here, successful puffing (a measurable outcome) is the best choice because it directly reflects the effect of flour type. Other options are either irrelevant or represent controlled variables.

Key Concept: Scientific Method, Controlled Experiments

c) Thickness of the rolled dough
[Solution Description]
To ensure a controlled experiment, only the independent variable (oil temperature) should change, while all other factors affecting puri puffing must remain constant. These include dough thickness, flour type, rolling method, and frying duration (as long as it is not part of the dependent variable). The solution involves identifying the factor that should be held constant.

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: 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: 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: Making Observations

c) A distinct sweet smell during fermentation
[Solution Description]
Qualitative observations are descriptive and involve characteristics that cannot be measured numerically. In a yeast fermentation experiment, noting the smell or bubble formation would be qualitative, while measuring gas volume would be quantitative.

Key Concept: Controlled Experimentation

b) Dough thickness
[Solution Description]
To ensure accuracy in experimentation, only one variable (here, oil temperature) should be changed at a time while other factors (dough thickness, dropping method) must remain constant. This is explicitly mentioned in the syllabus.

Key Concept: Scientific Investigation Approach

b) Ask a scientific question about the phenomenon
[Solution Description]
The first step in any scientific investigation is to ask a clear and specific question. According to the syllabus, this involves identifying what you want to investigate, such as understanding why a puri puffs up when fried. The other steps (identifying variables, conducting experiments, etc.) come later.

Key Concept: Observation and Experimentation

c) To determine which single factor causes the puffing
[Solution Description]
Changing only one variable at a time ensures that any observed effect can be directly attributed to that variable. This eliminates confusion caused by multiple changes affecting the outcome simultaneously, as per the systematic approach described in the syllabus.

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, Observation

c) Calculating the ratio of final expanded volume to initial dough volume
[Solution Description]
Quantitative measurement requires numerical data. Among the options, measuring the final volume ratio (puffed vs unpuffed state) provides the most direct and objective quantitative measurement of puffing degree.
Calculation approach:
1) Measure initial dough ball diameter ($D_i$)
2) After frying, measure puffed puri height ($H_p$) and width ($W_p$)
3) Volume ratio = \[
R=
\frac{\pi \left(\frac{W_p}{2}\right)^2 H_p}
{\frac{4}{3}\pi \left(\frac{D_i}{2}\right)^3}
\]
4) Higher ratio indicates better puffing
Other options either lack quantification (visual inspection) or measure indirect aspects (time).

Key Concept: Effect of Dough Thickness

c) Moderately thin dough results in one side being thinner than the other
[Solution Description]
The puffing of a puri depends on how steam gets trapped inside the rolled dough. A thicker dough may not allow uniform expansion, while a thinner one puffs more easily due to rapid vaporization of moisture and thin layers separating quickly. Therefore, an extremely thick dough might not puff properly compared to a moderately thin one.

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: 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: 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: 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: 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: Controlling Variables

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that oil temperature affects puri puffing, which is true as higher temperatures cause faster water evaporation from the dough. The reason correctly explains this phenomenon by linking higher oil temperatures to quicker evaporation and puffing. Thus, both are true, and the reason accurately explains the assertion.

Key Concept: Controlling variables and measuring changes

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that excessive oil temperature prevents proper puffing of the puri, which is true because high heat causes rapid surface hardening. The Reason explains this phenomenon by stating that quick cooking traps steam, hindering uniform expansion, which is scientifically accurate and directly justifies the Assertion.
Experimentally, if oil is too hot, moisture inside the dough turns to steam but cannot escape due to the hardened crust, leading to uneven puffing or no puffing at all. Thus, both statements are true, and the Reason correctly explains the Assertion.

Key Concept: Hypothesis Formation and Testing

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The Assertion states that uniform thinness leads to greater puffing due to even steam expansion. This is true as thinner dough allows uniform heat penetration, creating steam evenly throughout. The Reason explains that dough thickness impacts heat distribution, affecting steam formation—which is also scientifically valid. However, while both statements are correct, the Reason does not directly explain why uniform thinness causes more puffing; it only links thickness to heat distribution. Hence, the Reason does not correctly justify the Assertion.

Key Concept: Hypothesis formation, variables control

c) Dough thickness and type of flour
[Solution Description]
To isolate the effect of oil temperature on puffing time, all other variables must be controlled (kept constant). These include:
1. Dough thickness - affects heat penetration rate.
2. Type of flour - changes dough elasticity and water content.
3. Method of dropping dough - influences initial heat distribution.
Only oil temperature should be varied as per the hypothesis.

Key Concept: Vapor pressure

c) Formation and expansion of steam bubbles inside the dough
[Solution Description]
As the puri is submerged in hot oil, the moisture inside turns into steam, creating vapor pressure. This trapped steam expands the dough, causing it to puff up due to bubble formation and expansion dynamics.

Key Concept: Experimental design, pressure-temperature relationship

b) Pressure becomes half
[Solution Description]
Given $P \propto \frac{T}{V}$:
1. Temperature ($T$) is constant (given)
2. Final volume $V_f = 2V_i$
3. Thus pressure ratio $\frac{P_f}{P_i} = \frac{T/V_f}{T/V_i} = \frac{V_i}{V_f} = \frac{1}{2}$
The pressure reduces to half its initial value when volume doubles at constant temperature.

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: Control Variables

b) Oil temperature and frying method
[Solution Description]
To ensure accurate and fair results, all variables except the one being tested (here, dough thickness) must remain constant. These are called control variables. Examples include oil temperature, frying method, and type of flour.

Key Concept: Analysis and Conclusion from Data

a) Puffing time increases with increasing dough thickness
[Solution Description]
The table shows that as dough thickness increases, puffing time also increases. Thin dough takes 5 seconds, medium takes 10, and thick takes 20. This suggests a direct proportional relationship ($\text{Puffing Time} \propto \text{Dough Thickness}$). Thus, option a) is correct.

Key Concept: Assertion-Reason

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 rolled dough affects the puffing of the puri. This is true because experiments show that thinner dough tends to puff up more easily. The reason given is that thinner dough allows steam to expand more easily, which is scientifically valid as steam expansion ($V \propto T$) is a key factor in puffing. Additionally, the reason correctly explains why the assertion is true, as it links dough thickness to steam expansion. Hence, both are true, and the reason is the correct explanation of the assertion.

Key Concept: Independent and Dependent Variables

b) Dough thickness
[Solution Description]
According to the key principle, when studying the effect of one independent variable (oil temperature), all other variables must be kept constant. Therefore, factors such as dough thickness, flour type, and dropping method must remain unchanged during the experiment.

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: Controlled variables, Observational outcomes

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that higher oil temperature reduces the puffing time of a puri, which is true because increased thermal energy accelerates the vaporization of water in the dough, leading to quicker expansion. The reason correctly explains this phenomenon by stating that higher oil temperature improves heat transfer, which directly affects the puffing time. Thus, both the assertion and reason are true, and the reason explains the assertion.

Key Concept: Identifying Variables

b) The conditions that can be deliberately changed
[Solution Description]
In an experiment, the researcher can deliberately change certain factors to observe their effect. These are called controlled variables or independent variables. Examples include thickness of rolled dough, type of flour used, temperature of oil, etc.

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: 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: Variables in Experiments

d) The variable that is deliberately changed by the experimenter
[Solution Description]
An independent variable is the variable that is deliberately changed or manipulated in an experiment to observe its effect on the dependent variable. For example, in the puri puffing experiment, the thickness of the dough is an independent variable because it can be changed to see how it affects puffing.

Key Concept: Variables in Experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that dough thickness is the independent variable in the given experiment, which is true because it is the variable being deliberately altered (e.g., rolled to different thicknesses) to study its impact on puffing behavior. The reason correctly explains why thickness is considered the independent variable—it is the one being manipulated to observe changes in the dependent variable (puffing). Thus, both Assertion and Reason are true, and Reason provides the correct explanation for Assertion.

Key Concept: Data Interpretation, Drawing Conclusions

c) Plant growth is maximum at 25% fertilizer concentration
[Solution Description]
The data shows initial increase in height with 25% fertilizer, but higher concentrations reduce growth. Optimal growth occurs at 25%, suggesting excessive fertilizer inhibits growth.

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: Experimental Variables and Conclusions

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 allows scientists to attribute effects to that variable, which is correct because isolating variables eliminates confounding factors. The reason explains why changing multiple variables complicates identifying causation, which directly supports the assertion. Thus, both are true, and the reason correctly explains the assertion.

Key Concept: Controlling Variables and Drawing Conclusions

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that accurate recording of experimental data is essential for drawing valid scientific conclusions. This is true because without precise records, the results cannot be verified or replicated. The reason explains that detailed observations help identify patterns and relationships between variables, which is crucial for reliable conclusions. Since the reason correctly justifies the assertion, both are true and the reason is the correct explanation.

Key Concept: Observation and Measurement

b) Asking focused questions
[Solution Description]
The first step in any scientific investigation is to ask focused questions based on observations. This helps in forming hypotheses and designing experiments.

Key Concept: Variable Control, Observation in Experiments

c) It complicates identifying which change affects the outcome
[Solution Description]
Scientific experiments require changing one variable at a time to isolate its effect. Changing both oil temperature and dough thickness simultaneously makes it impossible to determine which variable caused any observed changes in puffing behavior.

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: Scientific Principles

b) To ensure clear and reliable results
[Solution Description]
Changing only one variable ensures that any observed effects can be directly attributed to that variable, maintaining accuracy and reliability of results.

Key Concept: Controlled variables, Observational variables

c) Time taken for the puri to puff up
[Solution Description]
The dependent variable is the one that is observed or measured as a result of changing the independent variable (thickness of dough). Here, the dependent variable would be whether the puri puffs up, time taken to puff up, or changes in texture since these are responses being measured.

Key Concept: Controlled Variables

b) To avoid changing multiple variables at once
[Solution Description]
In a controlled experiment, only one variable (independent variable) should be changed at a time while keeping all others constant (controlled variables). If the thickness of the dough varies, it could affect the puffing independently of the oil temperature, making it difficult to isolate the effect of temperature alone.

Key Concept: Variables in Experiments

c) Time taken for the puri to puff up
[Solution Description]
The dependent variable is what is measured or observed in response to changes in the independent variable. Here, the puffing of puris (whether it puffs up or not, or the time taken to puff) depends on other variables like temperature or thickness of the dough and hence is the dependent variable.

Key Concept: Observation and Measurement

c) To understand additional aspects of the phenomenon
[Solution Description]
Sensory details like smell, sound, or visual changes provide additional qualitative data that can help explain the phenomenon being studied. They complement quantitative measurements (e.g., time taken to puff) by offering insights into underlying processes, such as oil degradation or moisture evaporation.

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 and Observation

b) Ask a scientific question based on observations
[Solution Description]
The first step in conducting a scientific investigation is to ask a scientific question based on observations. This helps in identifying what needs to be studied or tested.

Key Concept: Controlled Experimentation

b) To ensure the effect is due to that specific variable
[Solution Description]
Changing only one variable at a time ensures that any observed effect can be directly attributed to that specific variable, making the experiment reliable and conclusions valid.

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: Systematic Investigation

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description] The syllabus states that keeping notes of everything observed during an experiment is essential for systematic investigation (Assertion A). It also mentions that while performing experiments, it is better to change only one thing at a time (Reason R). Both statements are true, but Reason R does not explain why keeping notes is a part of systematic investigation. Therefore, the correct answer is b).

Key Concept: Systematic Recording, Anomalies, Pattern Identification

b) The omission hides whether differences in puffing times are due to pricking or other factors.
[Solution Description]
Pricking holes can significantly alter puffing behavior. Without recording which puris were pricked, the scientist cannot distinguish if variations in puffing times are due to other experimental conditions or this unrecorded change. This leads to potential misidentification of patterns or anomalies in the data.

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: Measurement Precision, Variable Isolation, Consistency

b) To ensure that differences in puffing are only due to dough freshness.
[Solution Description]
Keeping oil temperature and frying method constant ensures that any observed differences in puffing are solely due to the dough's freshness. If these variables change, the effects of freshness cannot be isolated, making the comparison unreliable and the conclusions invalid.

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: Scientific Investigation

c) To isolate the effect of one specific factor on the outcome
[Solution Description]
Controlling variables helps isolate the effect of one specific factor on the outcome. By changing only one variable at a time while keeping others constant, we can accurately determine how that single variable influences the puffing of the puri. This ensures reliable and valid results.

Key Concept: Effect of Dough Thickness on Puri Puffing

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that a thinner layer of dough results in a puffier puri when fried in hot oil, which is true because thinner dough cooks faster and creates an even steam pressure distribution, leading to better puffing. However, the reason given is incorrect because thinner dough does not allow steam to escape more easily; instead, it traps steam effectively, causing puffing. Thus, the assertion is true, but the reason is false.

Key Concept: Variables, Controlled Experimentation

d) Assertion is false, but Reason is true.
[Solution Description]
First, let's analyze the Assertion: While it's true that thicker dough may initially seem to trap more steam, excessive thickness can prevent uniform heating and lead to uneven puffing or no puffing at all. Thus, the Assertion is not universally correct. Next, the Reason is scientifically accurate—the puffing occurs due to water vaporization creating steam pockets within the dough. Therefore, while the Reason is true, it does not correctly explain the Assertion, as the Assertion itself is false under certain conditions.

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: 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: Real-world applications, Pressure

c) Assertion is true, but Reason is false.
[Solution Description]
The puffing up of a puri occurs because the water content in the dough vaporizes into steam when heated, creating pressure inside the dough. This pressure causes the dough to expand, but the reason for uneven expansion is not just the pressure difference—it’s also due to structural weaknesses or thin spots in the dough. Thus, while the assertion correctly identifies the role of steam, the reason incorrectly attributes the uneven swelling solely to pressure differences without accounting for structural variations in the dough. Therefore, Assertion is true, but Reason is false.

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: 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: Pressure and Weather Events

c) A small pressure difference causes slow air movement (breeze), while a larger difference causes faster movement (strong winds/cyclones).
[Solution Description]
Air moves from regions of high pressure to low pressure due to the pressure gradient force. A small pressure difference results in a slow movement of air, causing a gentle breeze. A larger pressure difference accelerates the air more, leading to stronger winds or cyclones. The greater the difference, the faster the air moves to balance the pressure.

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.

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.