CBSE Class 7 Science Chapter 5: Changes Around Us: Physical and Chemical — Assertion & Reason
CBSE Class 7 Science Assertion & Reason
Expert crafted · Instant PDF download · 2026-27
The following Assertion and Reason questions are based on Chapter 5: Changes Around Us: Physical and Chemical from the NCERT Class 7 Science textbook Curiosity. 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): Tearing a piece of paper into small pieces is a physical change.
Reason (R): In a physical change, only physical properties like shape and size change, and no new substance is formed.
Reason (R): In a physical change, only physical properties like shape and size change, and no new substance is formed.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Even though the paper is in smaller pieces, it is still paper; no new chemical substance has been created.
2
Assertion (A): When carbon dioxide is passed through lime water, it turns milky.
Reason (R): The milky appearance is due to the formation of a new insoluble substance called calcium carbonate.
Reason (R): The milky appearance is due to the formation of a new insoluble substance called calcium carbonate.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The chemical reaction between carbon dioxide and calcium hydroxide (lime water) yields calcium carbonate, which makes the liquid look cloudy or milky.
3
Assertion (A): Mixing baking soda with vinegar produces a fizzing sound and gas bubbles.
Reason (R): The gas produced during this chemical reaction is oxygen.
Reason (R): The gas produced during this chemical reaction is oxygen.
Answer: (c)
A is true, but R is false. Mixing baking soda and vinegar does produce bubbles and a fizzing sound, but the gas released is carbon dioxide, not oxygen.
4
Assertion (A): The burning of a magnesium ribbon is a chemical change.
Reason (R): It produces heat, light, and a new substance called magnesium oxide.
Reason (R): It produces heat, light, and a new substance called magnesium oxide.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Because a completely new substance (magnesium oxide powder) is formed during the burning process, it is classified as a chemical change.
5
Assertion (A): Rusting of iron is considered a physical change.
Reason (R): During rusting, iron reacts with oxygen and moisture to form a new brown-coloured substance called rust.
Reason (R): During rusting, iron reacts with oxygen and moisture to form a new brown-coloured substance called rust.
Answer: (d)
A is false, but R is true. Rusting is a chemical change, not a physical change, precisely because it involves a chemical reaction that forms a new substance (iron oxide).
6
Assertion (A): A chemical reaction in which a substance reacts with oxygen to produce heat and/or light is called combustion.
Reason (R): Wood, paper, and kerosene are examples of combustible substances.
Reason (R): Wood, paper, and kerosene are examples of combustible substances.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. While both statements are factual, listing examples of combustible materials does not explain the scientific definition of combustion.
7
Assertion (A): A burning candle extinguishes shortly after being covered with an inverted glass tumbler.
Reason (R): The glass tumbler cuts off the continuous supply of oxygen required for combustion.
Reason (R): The glass tumbler cuts off the continuous supply of oxygen required for combustion.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Oxygen is an essential component of the fire triangle; without it, the flame cannot survive and goes out.
8
Assertion (A): A piece of paper catches fire when sunrays are focused on it using a magnifying glass for some time.
Reason (R): Focusing sunrays heats the paper until it reaches its ignition temperature, the minimum temperature at which it catches fire.
Reason (R): Focusing sunrays heats the paper until it reaches its ignition temperature, the minimum temperature at which it catches fire.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Combustible substances need to reach a specific heat threshold (ignition temperature) to burn, which the concentrated solar energy provides.
9
Assertion (A): The burning of a candle involves only chemical changes.
Reason (R): The melting of solid wax into liquid wax is a physical change, while the burning of wax vapour is a chemical change.
Reason (R): The melting of solid wax into liquid wax is a physical change, while the burning of wax vapour is a chemical change.
Answer: (d)
A is false, but R is true. A burning candle involves both physical changes (melting and evaporation of wax) and chemical changes (combustion of wax vapour).
10
Assertion (A): The melting of an ice cube and the boiling of water are reversible changes.
Reason (R): We can freeze water back into ice and condense water vapour back into liquid water.
Reason (R): We can freeze water back into ice and condense water vapour back into liquid water.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Changes in the physical state of water do not alter its chemical composition and can be easily reversed by cooling or heating.
11
Assertion (A): Making popcorn from corn kernels is an irreversible change.
Reason (R): The popped corn cannot be returned to its original kernel form.
Reason (R): The popped corn cannot be returned to its original kernel form.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The heat permanently changes the structure of the corn, making it impossible to reverse the process.
12
Assertion (A): The rusting of iron bridges and the decaying of stored food are desirable changes.
Reason (R): Some changes in our daily life are useful, while others cause damage and are undesirable.
Reason (R): Some changes in our daily life are useful, while others cause damage and are undesirable.
Answer: (d)
A is false, but R is true. Rusting and food decay cause structural damage and waste, making them highly undesirable changes.
13
Assertion (A): The decomposition of food is always an undesirable change in every situation.
Reason (R): Decomposition of food waste is highly desirable and useful when converting it into nutrient-rich compost.
Reason (R): Decomposition of food waste is highly desirable and useful when converting it into nutrient-rich compost.
Answer: (d)
A is false, but R is true. While food rotting in the fridge is undesirable, the same process is highly desirable when creating compost for gardening.
14
Assertion (A): Weathering of rocks to form soil takes place very rapidly within a few weeks.
Reason (R): Weathering involves physical and chemical changes caused by temperature, water, and tree roots over thousands of years.
Reason (R): Weathering involves physical and chemical changes caused by temperature, water, and tree roots over thousands of years.
Answer: (d)
A is false, but R is true. Weathering is a remarkably slow natural process that breaks down massive rocks into soil over millennia, not weeks.
15
Assertion (A): The continuous erosion of river rocks and pebbles by flowing water makes them appear smoother over time.
Reason (R): Erosion is a chemical change where rocks react with the flowing water to form new smooth substances.
Reason (R): Erosion is a chemical change where rocks react with the flowing water to form new smooth substances.
Answer: (c)
A is true, but R is false. While flowing water does smooth rocks, erosion is a physical change where materials are mechanically worn away and moved, not a chemical reaction forming new substances.
16
Assertion (A): Fire can be started simply by having a combustible fuel and sufficient oxygen present in the air.
Reason (R): Heat must also be supplied to raise the fuel's temperature to its ignition point to start combustion.
Reason (R): Heat must also be supplied to raise the fuel's temperature to its ignition point to start combustion.
Answer: (d)
A is false, but R is true. Fuel and oxygen alone are not enough to start a fire; heat is the crucial third component of the fire triangle required to trigger ignition.
17
Assertion (A): Wrapping a thick blanket around a person whose clothes have caught fire is an effective way to extinguish the flames.
Reason (R): The blanket lowers the ignition temperature of the person's clothes.
Reason (R): The blanket lowers the ignition temperature of the person's clothes.
Answer: (c)
A is true, but R is false. A blanket works because it cuts off the supply of oxygen, breaking the fire triangle. It does not alter the ignition temperature of the clothes.
18
Assertion (A): The evaporation of water from seas and oceans due to the heat of the Sun is a physical change.
Reason (R): During evaporation, the liquid water merely changes its state into water vapour without forming any new chemical substance.
Reason (R): During evaporation, the liquid water merely changes its state into water vapour without forming any new chemical substance.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Since H₂O remains H₂O whether it is a liquid or a gas, phase changes like evaporation are strictly physical changes.
19
Assertion (A): Fireflies emit light in the dark through a process called bioluminescence.
Reason (R): The light produced by fireflies is a result of a physical change inside their bodies.
Reason (R): The light produced by fireflies is a result of a physical change inside their bodies.
Answer: (c)
A is true, but R is false. Bioluminescence in fireflies is actually the result of a chemical change that naturally produces light without heat.
20
Assertion (A): Blowing exhaled air through a straw into normal tap water creates bubbles but does not turn the water milky.
Reason (R): Tap water lacks the calcium hydroxide (lime water) needed to react with exhaled carbon dioxide and form insoluble calcium carbonate.
Reason (R): Tap water lacks the calcium hydroxide (lime water) needed to react with exhaled carbon dioxide and form insoluble calcium carbonate.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. The specific chemical reaction that turns the liquid milky only occurs between carbon dioxide and lime water, which is why tap water remains clear.
❓ Frequently Asked Questions
What is covered in CBSE Class 7 Science Chapter 5 Changes Around Us: Physical and Chemical?
This chapter covers all key topics from Changes Around Us: Physical and Chemical as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 7 board exam preparation covering the complete syllabus.
Are these CBSE Class 7 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 7 Science?
All chapters of CBSE Class 7 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
Can I study Changes Around Us: Physical and Chemical online for free?
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