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 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: 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: 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, 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: 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 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 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: 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: 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: 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 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: Controlled Experiment

d) To establish a clear cause-and-effect relationship
[Solution Description]
Changing only one variable at a time ensures that any observed effect can be directly attributed to that specific variable. This helps in establishing a cause-and-effect relationship and eliminates confusion from multiple variables affecting the outcome simultaneously.

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: 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 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: 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 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: 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: 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 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: Systematic Investigation, Data Recording

b) Uncontrolled minor variations in dough preparation or oil heating
[Solution Description]
Inconsistent results in a controlled experiment often stem from unaccounted variables or measurement errors. Potential issues include slight variations in dough preparation (e.g., uneven kneading), inconsistent oil temperature maintenance, or subjective judgment of "puffing." Proper calibration of instruments and standardized protocols are critical to minimize such errors.

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: 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 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: 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: Controlled Experiments, Iterative Process

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion claims that changing multiple variables simultaneously speeds up finding causal relationships, which is false because doing so introduces ambiguity in identifying which variable caused the observed effect. The Reason is true because controlling one variable at a time isolates its impact, eliminating other influences.
Therefore, the Assertion is false, but the Reason is true.

Key Concept: Controlled Experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that changing one variable at a time helps identify cause-and-effect relationships, which is true as it isolates the effect of that variable. The reason explains why this is done—by keeping other variables constant, we ensure that any change in the outcome is solely due to the manipulated variable. 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: Analysis and Conclusion

c) $t_{puff} \propto \frac{1}{T_{oil}}$
[Solution Description]
The given relationship shows that $t_{puff}$ is inversely proportional to $T_{oil}$. As $T_{oil}$ increases, $t_{puff}$ decreases, following the hypothetical equation: $t_{puff} \propto \frac{1}{T_{oil}}$. Hence, the correct choice reflects this inverse proportionality.

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: Variables identification, Experimental design

a) Type of oil used for frying
[Solution Description]
An extraneous variable is one that could affect the dependent variable but isn't the focus of the study. For this experiment about dough thickness and puffing: The independent variable is dough thickness, the dependent variable is puffing behavior. We need to control variables like oil temperature, cooking time, and flour type that could also affect puffing but aren't being studied.

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: 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: 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

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, 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: 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: 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: 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: Observation

d) The thin side expands due to trapped steam pressure
[Solution Description]
When a puri is dropped into hot oil, steam forms inside due to trapped moisture. The steam pushes upwards against the thinner side first, causing it to inflate more while the thicker side remains denser. This makes one side appear thinner than the other.

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: 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: 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: Measuring Changes

c) Whether the puri puffs up or not
[Solution Description]
Dependent variables are outcomes that are measured in response to changes in the independent variable. Here, the dependent variables include whether the puri puffs up, time taken to puff up, and the thickness of the fried puri, as these are the results observed based on oil temperature variations.

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: 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: Experimental approach

c) Alter only one variable while keeping others constant
[Solution Description]
In a controlled experiment, only one variable should be changed at a time while keeping all other factors constant to isolate its effect. This ensures the results are attributable to that specific variable.

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 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: 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: Designing and Conducting Experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In an experiment, controlled variables are kept constant to isolate the effect of the independent variable (here, oil temperature) on the dependent variable (puri puffing). The assertion states that keeping dough thickness constant is essential, which is correct because it prevents this factor from affecting puffing results. The reason explains why controlling variables is necessary—to ensure only the independent variable influences the outcome. Therefore, both Assertion and Reason are true, and Reason correctly explains the Assertion.

Key Concept: Variables in an Experiment

b) Oil temperature
[Solution Description]
The independent variable is the factor that is deliberately changed or manipulated in an experiment to observe its effect. Here, the experiment aims to study how changing oil temperature affects puffing time. Therefore, the oil temperature is the independent variable.

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: 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: 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: Controlled Experiment Design

b) Keeping all variables except flour type constant
[Solution Description]
To isolate the effect of flour type (independent variable), other variables (like oil temperature, dough thickness, and dropping method) must be controlled (kept constant). This prevents interference with the observed result.

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: 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: 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: 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: 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: Systematic Experimentation

d) Dough thickness
[Solution Description]
When testing different dough thicknesses while keeping oil temperature constant, the independent variable is the dough thickness. The study aims to understand how this specific change impacts puffing, making it the primary factor under investigation.

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: Drawing Conclusions

d) The recorded data to find patterns or relationships
[Solution Description]
Analyzing recorded data to identify patterns or relationships helps form logical conclusions based on observations.

Key Concept: Experimental Design, Variables

b) Enzyme concentration
[Solution Description]
Control variables must be kept constant to isolate the effect of pH. Enzyme concentration affects activity directly, so it cannot be a control variable when studying pH effects.

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: 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: Observation and Measurement, SI Units

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that changing the unit (km/h to m/s) affects only the numerical value, not the physical interpretation. This is correct because the physical quantity (speed) remains unchanged; only its representation changes.
The Reason explains that unit conversion involves a constant factor, preserving the physical meaning. This is also true since $1 \, \text{km/h} = \frac{1000 \, \text{m}}{3600 \, \text{s}} \approx 0.2778 \, \text{m/s}$.
Further, the Reason correctly justifies the Assertion because the constant factor ensures the underlying physical interpretation (speed) remains consistent regardless of the unit. Thus, both Assertion and Reason are true, and the Reason explains the Assertion.

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: 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: Measuring responses in experiments

c) Change in the dough’s thickness
[Solution Description]
To determine whether a puri has puffed up completely, we need to observe measurable responses such as whether the puri puffs up (yes/no), the time taken to puff up, or changes in thickness. Among these, checking whether the puri puffed up (yes/no) is a direct observation, while measuring the change in thickness provides quantitative data about the extent of puffing.
The correct answer is "Change in the dough’s thickness" as it gives a measurable response indicating complete puffing.

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: 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: 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: 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: Systematic investigation, Measurement control in experiments

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that controlling only one variable at a time is essential for determining causality, which is true as per the syllabus's emphasis on systematic investigation. The reason explains why this is necessary—if multiple variables change together, the cause-effect relationship cannot be isolated, making the reason both true and the correct explanation of the assertion.

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: Recording Observations

c) Maintaining detailed notes of all sensory and measurable changes during the process
[Solution Description]
Detailed and accurate records are crucial for scientific investigations. Observations should include both qualitative (e.g., color change, puffing sound) and quantitative measurements (e.g., dough thickness, frying duration). Recording sensory details like smell or texture also aids in comprehensive analysis.

Key Concept: Systematic Observation, Data Analysis

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that systematic recording of both qualitative and quantitative data ensures reproducibility in experiments. This is true because detailed documentation allows others to replicate the experiment under the same conditions. The reason explains why both types of data are essential: quantitative data provides numerical measurements (e.g., time taken, temperature), while qualitative data describes observations (e.g., color change, texture). Since the reason correctly explains why systematic recording of both types ensures reproducibility, the correct option is a).

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: 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: 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: Scientific Method

c) Ask a scientific question
[Solution Description]
The scientific method begins with asking a clear, testable question about the phenomenon being observed. For example, "What factors affect how a puri puffs up when fried?" This guides further investigation.

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: Observation and Curiosity in Everyday Life, Designing Simple Experiments

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion correctly states that observing a puri puffing up is an example of applying scientific inquiry to everyday phenomena. However, the reason provided is false because the puffing of a puri depends on multiple factors such as dough thickness, oil temperature, and moisture content, not just the thickness of the dough alone. Therefore, while the assertion is true, the reason is false.

Key Concept: Ecosystems and Environmental Balance, Climate Change and Solutions

b) Wolves stabilize at 25 due to reduced prey
[Solution Description]
In a balanced ecosystem, predator-prey dynamics follow a direct relationship. With 1000 deer supporting 50 wolves, the ratio is 20:1 (deer:wolves). If deer reduce by 50% to 500, the wolf population will eventually decline proportionally to maintain balance.
Assuming the same ratio, 500 deer would sustain approximately 25 wolves ($500 / 20 = 25$) after several generations due to reduced prey availability. This demonstrates how disruptions in one part of an ecosystem cascade through trophic levels.

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: Air Pressure, Weather Phenomena

b) Cyclone formation becomes less likely
[Solution Description]
Cyclones form due to differences in air pressure, where warm, moist air rises and creates a low-pressure zone.
Step 1: In a region already experiencing very low pressure, the pressure gradient between surrounding areas and the center reduces.
Step 2: Reduced pressure gradient weakens wind speeds and disrupts cyclone formation.
Therefore, cyclones are less likely to form or intensify in regions with very low atmospheric 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: 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: 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: 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.