CBSE Class 9 Science Chapter 1: Exploration: Entering the World of Secondary Science — Assertion & Reason
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The following Assertion and Reason questions are based on Chapter 1: Exploration: Entering the World of Secondary Science from the NCERT Class 9 Science textbook. Each question has four options — read both the Assertion (A) and Reason (R) carefully before selecting your answer.
How to attempt Assertion & Reason questions:
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Assertion & Reason Questions
1
Assertion (A): Science uses models to make sense of the complex natural world.
Reason (R): Models include every single microscopic detail of a real system to ensure absolute accuracy.
Reason (R): Models include every single microscopic detail of a real system to ensure absolute accuracy.
Answer: (c)
A is true, but R is false. Models deliberately ignore certain details to focus only on what is most important for a given question.
2
Assertion (A): When studying the motion of a falling object, air resistance is sometimes neglected.
Reason (R): Ignoring complex details is done on purpose to keep things simple enough to understand basic effects like gravity.
Reason (R): Ignoring complex details is done on purpose to keep things simple enough to understand basic effects like gravity.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. This simplification is a core part of building scientific models.
3
Assertion (A): Words like 'force', 'work', and 'cell' have very specific meanings in science compared to everyday life.
Reason (R): Scientific ideas must be communicated clearly and unambiguously across the world.
Reason (R): Scientific ideas must be communicated clearly and unambiguously across the world.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Science uses a precise, shared language to allow scientists to compare results and build ideas together.
4
Assertion (A): The speed of light is denoted by the symbol 'c'.
Reason (R): The symbol comes from the Latin word celeritas, meaning speed.
Reason (R): The symbol comes from the Latin word celeritas, meaning speed.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Scientific symbols often come from history and international agreements.
5
Assertion (A): Standard units like the kilogram are used globally instead of local measurement systems.
Reason (R): Standard units allow scientific results to be compared and ensure fairness in daily life and trade.
Reason (R): Standard units allow scientific results to be compared and ensure fairness in daily life and trade.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Universal standards avoid the confusion and errors that would arise from using different local weights.
6
Assertion (A): Mathematics in science is merely a mechanical calculation tool.
Reason (R): An equation is a compact statement about how certain physical quantities are related to one another.
Reason (R): An equation is a compact statement about how certain physical quantities are related to one another.
Answer: (d)
A is false, but R is true. Mathematics is not just a calculation tool or a hurdle; it is a powerful language that helps us think clearly about the world.
7
Assertion (A): A scientific law describes a regular pattern observed in nature.
Reason (R): A scientific theory provides an explanation of why those natural patterns occur.
Reason (R): A scientific theory provides an explanation of why those natural patterns occur.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both statements correctly define key scientific terms, but one does not explain the other.
8
Assertion (A): A scientific theory is just a guess or an untested idea.
Reason (R): Scientific theories are always open to improvement and change as new evidence becomes available.
Reason (R): Scientific theories are always open to improvement and change as new evidence becomes available.
Answer: (d)
A is false, but R is true. A theory is an explanation based on careful testing and evidence, not a simple guess, though it remains open to revision.
9
Assertion (A): The failure of a scientific prediction is considered a great strength of science.
Reason (R): When predictions fail, scientists are forced to re-examine their assumptions, models, or measurements based on evidence.
Reason (R): When predictions fail, scientists are forced to re-examine their assumptions, models, or measurements based on evidence.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Science's openness to being corrected by nature itself is what makes it reliable.
10
Assertion (A): Weather forecasts are highly reliable for several months into the future.
Reason (R): Weather depends on changing factors where very tiny differences can grow over time and lead to completely different outcomes.
Reason (R): Weather depends on changing factors where very tiny differences can grow over time and lead to completely different outcomes.
Answer: (d)
A is false, but R is true. Because complex systems are sensitive to tiny changes, forecasts are only reliable for a few hours or days.
11
Assertion (A): Making rough estimates is an important scientific skill.
Reason (R): An approximate estimate is often enough to tell us whether a result is reasonable or impossible.
Reason (R): An approximate estimate is often enough to tell us whether a result is reasonable or impossible.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Estimation helps build intuition, detect errors, and develop confidence in reasoning.
12
Assertion (A): Food becomes harmful and should not be eaten during a solar eclipse.
Reason (R): An eclipse is merely a play of shadows and involves no physical or chemical change that spoils food.
Reason (R): An eclipse is merely a play of shadows and involves no physical or chemical change that spoils food.
Answer: (d)
A is false, but R is true. There is no biological or chemical mechanism supporting the claim that food becomes harmful during the shadow of an eclipse.
13
Assertion (A): Meghnad Saha treated the matter in stars as a hot gas and ignored complex atomic movements.
Reason (R): This simplification allowed him to explain how the colour of stars is deeply connected to their temperature.
Reason (R): This simplification allowed him to explain how the colour of stars is deeply connected to their temperature.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. By simplifying the model, he could focus on the most important variables.
14
Assertion (A): Complex real-world problems like climate change can be fully solved using only one branch of science.
Reason (R): Real-world problems require ideas from physics, chemistry, biology, earth science, and mathematics together.
Reason (R): Real-world problems require ideas from physics, chemistry, biology, earth science, and mathematics together.
Answer: (d)
A is false, but R is true. The natural world has no strict boundaries; solving real problems demands an interdisciplinary approach.
15
Assertion (A): Understanding how a surgical mask works involves concepts from multiple scientific disciplines.
Reason (R): A mask relies on particle motion, polymer fibres, virus sizes, and airflow modelling.
Reason (R): A mask relies on particle motion, polymer fibres, virus sizes, and airflow modelling.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Mask functionality integrates physics, chemistry, biology, and mathematics.
16
Assertion (A): Predictions in science are essentially random guesses about future events.
Reason (R): Scientific predictions are reasoned expectations based on evidence, established models, and careful thinking.
Reason (R): Scientific predictions are reasoned expectations based on evidence, established models, and careful thinking.
Answer: (d)
A is false, but R is true. Scientific predictions are deeply rooted in prior knowledge and laws, not arbitrary guesswork.
17
Assertion (A): No scientific theory is ever final and none is beyond question.
Reason (R): Science continuously develops as people test ideas, gather new evidence, and learn from mistakes.
Reason (R): Science continuously develops as people test ideas, gather new evidence, and learn from mistakes.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Science is a continuous human activity shaped by questioning and new discoveries.
18
Assertion (A): The principle of conservation of energy is considered a scientific principle rather than a law.
Reason (R): Principles are broad ideas that help us make sense of specific given situations.
Reason (R): Principles are broad ideas that help us make sense of specific given situations.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The textbook distinguishes principles as broad guiding ideas applied to physical situations.
19
Assertion (A): A passenger aircraft once ran out of fuel mid-flight due to a mix-up in measurement units.
Reason (R): Using internationally agreed standard units (SI) everywhere avoids conversions and potentially dangerous errors.
Reason (R): Using internationally agreed standard units (SI) everywhere avoids conversions and potentially dangerous errors.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. The reason states a general benefit of SI units, while the assertion recounts a specific historical incident caused by ignoring them.
20
Assertion (A): Exact, precise calculations are always required before checking if an answer makes sense.
Reason (R): Estimation is a valuable scientific tool to detect errors early on.
Reason (R): Estimation is a valuable scientific tool to detect errors early on.
Answer: (d)
A is false, but R is true. Exact values are not always necessary early on; approximate estimation is highly valued to check if a result is reasonable.
❓ Frequently Asked Questions
What is covered in CBSE Class 9 Science Chapter 1 Exploration: Entering the World of Secondary Science?
This chapter covers all key topics from Exploration: Entering the World of Secondary Science as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 9 board exam preparation covering the complete syllabus.
Are these CBSE Class 9 Science Assertion & Reason updated for 2026-27?
Yes, all content at eBookPublisher is updated as per the latest 2026-27 CBSE syllabus.
How many chapters are in CBSE Class 9 Science?
All chapters of CBSE Class 9 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
Can I study Exploration: Entering the World of Secondary Science online for free?
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