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

b) Type of flour used
[Solution Description]
To investigate why one side of a puri is thinner systematically, it is essential to control variables. This means changing only one factor at a time while keeping others constant. Key variables to keep constant include:
1) Type of flour used (e.g., only atta or maida).
2) Size and thickness of the rolled dough.
3) Method of dropping the dough into the oil.
By keeping these variables consistent, we can accurately study the effect of the change in one variable (like temperature of oil) on the outcome.

Key Concept: Observation in Science

c) The puri puffed up completely
[Solution Description]
Qualitative observations describe characteristics or qualities that cannot be measured numerically. In the puri experiment, such observations include:
1) Whether the puri puffs up (yes/no).
2) Smell or smoke from the oil.
3) Splattering of oil.
Quantitative observations would involve measurable data like time or temperature.

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 Basics

c) Asking questions
[Solution Description]
The first step in scientific investigation is asking a question or expressing curiosity about something observed in nature or everyday life, as mentioned in the syllabus.

Key Concept: Scientific Curiosity

c) Curiosity about the world
[Solution Description]
The text emphasizes that curiosity is fundamental for scientific exploration, as shown by examples like observing puris puffing up and questioning natural phenomena. It states that all scientific experiments begin with curiosity.

Key Concept: Observation in Science

d) In everyday places like kitchens
[Solution Description]
The text specifically mentions that science is everywhere and gives examples of kitchen observations like puris puffing up. It states you don't need fancy equipment - even home kitchens are good places for observation.

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: 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: Focused Scientific Questions, Variables

d) How does increasing the oil temperature from 150°C to 200°C affect the time taken for the puri to fully puff?
[Solution Description]
To determine the most focused and testable question, we need one that clearly identifies both the independent variable (oil temperature) and the dependent variable (puffing of the puri). The question must also specify measurable outcomes. Among the options, "How does increasing the oil temperature from 150°C to 200°C affect the time taken for the puri to fully puff?" directly specifies the range of the independent variable and what is being measured (time taken).

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: 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 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: 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: 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: 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: 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 Inquiry, Hypothesis Testing

d) Assertion is false, but Reason is true.
[Solution Description]
In scientific inquiry, a hypothesis is an educated guess that provides a testable explanation for an observed phenomenon. It does not need to be proven true; rather, it serves as a starting point for investigation. Experiments are designed to gather evidence that either supports or refutes the hypothesis. The Reason correctly explains that the purpose of a hypothesis is to offer a testable explanation, not necessarily one that must be proven true. Therefore, the Assertion is false because a hypothesis can still be valuable even if experiments refute it, while the Reason is true and correctly describes the role of a hypothesis in science.

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: 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 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: 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: 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: 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 Observation

d) Making careful observations and asking questions
[Solution Description]
The first step in scientific inquiry is developing curiosity and making careful observations about natural phenomena. This leads to asking questions like "Why?" or "How?" which form the basis of further investigation.

Key Concept: Scientific Investigation, Variables

a) Thickness of the dough and oil temperature
[Solution Description]
In a controlled experiment where the effect of oil temperature is being tested, other variables must remain constant to isolate the impact of temperature. The thickness and size of the dough, type of flour ($atta$ or $maida$), and how the dough is dropped into the oil should all be kept the same. Only the oil temperature should vary.

Key Concept: Observation, Data Analysis

d) Higher temperatures generally improve puffing success rates
[Solution Description]
The data shows a higher success rate of puffing at 200°C compared to 160°C. This suggests a positive correlation between oil temperature and puffing success. However, since it's an observational result, causation cannot be definitively established without considering other variables like dough consistency or experimental errors.

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: Controlled Experiments

a) Thickness of the dough
[Solution Description]
The independent variable is the factor that is deliberately changed or manipulated in an experiment. In this case, the thickness of the dough is being altered to observe its effect on puri puffing. Therefore, the thickness of the dough is the independent variable.

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: 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: 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: 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 Inquiry Basics

c) Asking a scientific question
[Solution Description]
The first step in any scientific inquiry is to ask a question about the observed phenomenon. Based on the syllabus, science begins with curiosity and careful observation, followed by formulating a scientific question.

Key Concept: Investigating Everyday Phenomena

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a puri puffs up due to trapped steam, which is true because heating causes water in the dough to vaporize. The reason explains that this steam creates pressure, leading to expansion, which is scientifically accurate and directly explains the assertion. Both statements are correct and logically connected.

Key Concept: Variables, Heat Transfer

d) The hotter oil puri will start puffing sooner but may not expand as fully
[Solution Description]
Higher oil temperature leads to faster steam generation inside the dough, causing more rapid puffing. However, excessive heat can prematurely set the crust before full expansion occurs.
Detailed explanation:
1) Steam formation rate increases with temperature (higher heat transfer)
2) Faster steam pressure buildup causes quicker puffing initiation
3) But if too hot, outer layer cooks too fast, limiting expansion
4) Optimal puffing requires balanced steam generation and dough flexibility
5) Therefore slightly higher temp puri should puff faster but may achieve similar final size
So the correct answer describes this nuanced temperature effect.

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: 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: Dough Composition

d) Maida puris develop a distinctly thinner side compared to atta puris
[Solution Description]
Maida lacks bran and fiber, making the dough softer and less elastic than atta. This affects puffing because steam escapes differently—maida puris tend to be crispier but may not expand uniformly, often resulting in a thinner side due to weaker dough structure.

Key Concept: Dough thickness, Oil temperature

b) Heat distribution causes uneven expansion, making one side thinner
[Solution Description]
The uneven puffing of a puri is primarily due to the difference in heat distribution and dough thickness. When the puri is dropped into hot oil, the side touching the oil first starts heating up faster. The moisture inside the dough evaporates, creating steam which causes the puri to puff. The thicker side takes longer to cook and may not puff as much because the trapped steam escapes from the thinner side first. Additionally, the method of dropping the puri (angle, speed) affects how uniformly it cooks.

Key Concept: Flour type, Moisture content

b) Atta puffs better due to higher gluten and moisture retention
[Solution Description]
The type of flour affects the gluten content and moisture retention. Atta (whole wheat flour) has higher fiber and gluten compared to maida (refined flour). Higher gluten provides elasticity, allowing the dough to stretch and trap steam better, leading to better puffing. Maida-based dough may puff inconsistently due to lower gluten, causing uneven steam trapping. Fresh dough retains more moisture, aiding in steam generation for puffing, while stored dough may dry out.

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: 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: 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: Identifying variables, experimental observation

b) Oil temperature affects puffing rate but has an upper limit for optimal results
[Solution Description]
The controlled variables in this experiment are dough thickness and oil quantity, while the independent variable being changed is oil temperature. The observations show a relationship between temperature and puffing time (higher temp = faster puffing), but also reveal an upper limit where excessive temperature causes burning. This demonstrates that while temperature affects puffing rate, there's an optimal range beyond which quality degrades.

Key Concept: Variable control, scientific methodology

b) To ensure the results are solely due to flour type difference
[Solution Description]
In scientific experiments, controlling all variables except the one being tested (here, flour type) ensures that any observed differences in puffing can be conclusively attributed to the flour type alone. If other variables like oil temperature or dough thickness vary, they might influence the results, making it impossible to isolate the effect of flour type.

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: Hypothesis formation, Experimental variables

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that uniform dough thickness prevents puffing due to no steam pressure differential. This is false because puffing can still occur if steam accumulates uniformly inside and inflates the dough without escaping preferentially from one side. The Reason correctly explains why puffing happens in typical cases where one side is thinner—steam escapes unevenly, creating pressure differences. Thus, the Assertion is false, but the Reason is true.

Key Concept: Variables in Experiment

c) Independent variable
[Solution Description]
In an experiment, the independent variable is the one that is intentionally changed to study its impact. For example, changing the oil temperature while frying puris to see how it affects puffing time.

Key Concept: Data interpretation, multi-variable analysis

c) Higher temperature and lower thickness reduce puffing time
[Solution Description]
Analyzing the data step-by-step:
1. Comparing rows 1 & 2: At same temp (180°C), thicker dough (3mm vs 2mm) takes longer (6s vs 4s) → thickness increases time
2. Comparing rows 1 & 3: Same thickness (2mm), higher temp (200°C vs 180°C) reduces time (3s vs 4s) → temperature decreases time
3. Combined effect shows both variables significantly impact puffing time.

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: 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: 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: 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: 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: 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: what can be controlled and observed

(b) Type of flour and oil temperature
[Solution Description]
To ensure accuracy in this experiment, only one variable (dough thickness) should change while keeping all other factors constant. The controlled variables include type of flour, oil temperature, and method of dropping dough. Changing any of these would affect the observed outcome (puffing). The correct answer is the option that lists these variables as needing to remain unchanged.

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: 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: Experimental Variables, Observation, Systematic Investigation

c) Recording the time taken for the puri to puff up and checking if it puffs uniformly
[Solution Description]
To systematically study the effect of oil temperature, the student should change only one variable (oil temperature) while keeping others like dough thickness, flour type, and dropping method constant. The student can measure the time taken for the puri to puff up (quantitative observation) and whether it puffs uniformly (qualitative observation). This ensures a controlled experiment where the change in puffing behavior can be directly attributed to the oil temperature.

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: 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: 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: 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: Controlled Variables

c) Time taken to puff up
[Solution Description]
The dependent variable is what you measure or observe in response to changes in the independent variable. Here, oil temperature is the independent variable, and the time taken for the puri to puff up is the dependent variable because it changes based on the oil temperature.

Key Concept: Chemical Reactions

b) $\text{Amino acids} + \text{Sugars} \rightarrow \text{Browning} + \text{Flavor}$
[Solution Description]
The Maillard reaction occurs between amino acids and reducing sugars under heat, leading to browning and flavor development. This is different from caramelization (which involves only sugars) or simple steam formation ($H_2O_{(l)} \rightarrow H_2O_{(g)}$). Thus, the correct answer is the Maillard reaction.

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: 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: 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: 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: Multi-variable analysis, Measurement accuracy

d) Documenting time, puffing success, oil splatter, and smell for each trial
[Solution Description]
Reliable data collection requires systematic recording of all observable changes (such as sensory details), repeating trials, and noting environmental conditions that might affect the experiment.

Key Concept: Observing changes in experiments

b) Temperature of the oil
[Solution Description]
Controlled variables are factors that remain constant during an experiment to test the effect of changing one variable at a time. In the given context, the thickness and size of the rolled dough, type of flour used, temperature of the oil, and method of dropping the dough into the oil are controlled variables.
The option "Temperature of the oil" is one such controlled variable as it can be kept constant or changed systematically to observe its effect on puffing.

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: Observation and Measurement in Experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that when investigating why a puri puffs up, only one variable should be changed at a time. This is true because scientific experiments require controlled conditions to isolate the effect of individual factors. The reason explains that changing multiple variables at once complicates identifying the exact cause of the observed response, which correctly justifies the assertion. Therefore, both assertion and reason are true, and the reason is the correct explanation of the assertion.

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: 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: Systematic Investigation in Experiments

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 during an experiment ensures accurate results, which is true because this approach helps isolate the effect of that specific variable. The reason given is that altering multiple variables simultaneously makes it difficult to determine which change caused the observed effect, which correctly explains why changing one variable at a time is important for systematic investigation. Both the assertion and reason are true, and the reason provides the correct explanation for the assertion.

Key Concept: Observation, Measurement, Variables

b) The puri takes longer to puff up or does not puff at all
[Solution Description]
When oil temperature is too cold, it does not provide enough heat to rapidly vaporize the moisture in the dough. This results in slower or no puffing because steam generation is insufficient to create pressure for expansion. The correct answer is based on understanding the role of heat in generating steam for puffing.

Key Concept: Observation Importance

b) The sound of oil splattering and puffing of puris
[Solution Description] Observations in experiments include sensory details like splattering, smell, or smoke, which lead to deeper questions.

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: 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: 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: Experimental Control, Data Collection

b) Use the same oil temperature and dough thickness but test multiple puris for each storage condition.
[Solution Description]
To isolate the effect of storage time, all other variables (oil temperature, dough thickness, etc.) must remain constant. Testing multiple samples reduces random errors, and consistent measurements ensure comparability.

Key Concept: Scientific Variables, Experiment Design

c) Using the same dough circles and dropping method but varying the oil temperature.
[Solution Description]
To study the effect of oil temperature alone, all other variables must be kept constant. This means using identical dough circles (same thickness, size, and flour type), dropping them in the same way into oils at different temperatures, and measuring the puffing outcome.

Key Concept: Observation, Scientific Inquiry

b) Steam is seen escaping from the phulka as it swells.
[Solution Description]
Scientific hypotheses are based on observable phenomena that can be tested. The formation of steam inside the phulka due to heat causing expansion is a measurable and testable observation, unlike subjective experiences like taste or unrelated factors like utensil material.

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: 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: Electricity and Its Effects, Understanding Forces and Pressure

c) As heat is directly proportional to the square of the current
[Solution Description]
The heating effect of electric current is given by Joule's law: $H = I^2 R t$, where $H$ is the heat produced, $I$ is the current, $R$ is the resistance, and $t$ is the time. Here, heat is proportional to the square of the current. If the current ($I$) is doubled, the heat produced increases by four times because $(2I)^2 = 4I^2$. Thus, increasing the current significantly raises the heat output of the heater when resistance is constant.

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: 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: 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: 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: Solutions and Mixtures

c) Salt breaks into $Na^+$ and $Cl^-$ ions
[Solution Description]
When salt (sodium chloride, $NaCl$) dissolves in water, it breaks into ions: sodium ($Na^+$) and chloride ($Cl^-$). This occurs because water molecules surround and separate the salt crystals, allowing them to disperse in the solution.

Key Concept: Pressure, Mixtures and Solutions

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a sharp knife cuts better than a blunt knife due to higher pressure. This is correct because a sharp knife has a smaller surface area at its edge compared to a blunt knife. According to the formula for pressure ($P = \frac{F}{A}$), when force ($F$) remains constant, decreasing the area ($A$) increases the pressure ($P$).
The reason correctly explains the assertion by stating the relationship between pressure and area, which is indeed inverse proportionality as per the formula. Therefore, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Light Reflection, Refraction

b) Focal length increases
[Solution Description]
Focal length of a lens depends on the refractive index contrast between lens material and surrounding medium.
Step 1: Lensmaker's formula: $\frac{1}{f} = (n_{\text{lens}} - n_{\text{medium}}) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$
Step 2: In air, $n_{\text{medium}} = 1$, so $(1.52 - 1) = 0.52$.
Step 3: In glycerine, $n_{\text{medium}} = 1.47$, so $(1.52 - 1.47) = 0.05$.
Step 4: Since $(n_{\text{lens}} - n_{\text{medium}})$ decreases, $\frac{1}{f}$ decreases, meaning $f$ increases.
Hence, focal length increases when submerged in glycerine.