CBSE Class 7 Science Exemplar Chapter 6: Physical and Chemical Changes - NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 7 PDF

This chapter delves into the fundamental concepts of physical and chemical changes, crucial for Class 7 Science students. The NCERT Solutions for Chapter 6, 'Physical and Chemical Changes,' provide clear explanations and step-by-step solutions to multiple-choice questions. Students will learn to differentiate between physical changes, where the substance's form changes but not its identity, and chemical changes, which involve the formation of new substances. The solutions cover topics like rusting of iron, combustion, melting of wax, and the transformation of milk into curd. Understanding these changes is vital for comprehending various natural phenomena and industrial processes. These solutions are designed to aid students in grasping the core ideas, reinforcing their learning, and preparing effectively for their examinations by offering accurate and easy-to-understand answers.

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Quick info

Board	CBSE
Class	Class 7
Subject	Science Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 6

Chapter summary

Chapter 6 of the CBSE Class 7 Science Exemplar focuses on distinguishing between physical and chemical changes. The NCERT Solutions cover multiple-choice questions that test the understanding of these concepts. Key topics include identifying characteristics of physical changes (like melting) versus chemical changes (like burning or rusting), and recognizing indicators of chemical reactions such as color change, temperature variation, or gas evolution. The solutions also address practical examples like the rusting of iron and the process of milk turning into curd, offering clarity on why certain changes are irreversible.

Learning outcomes

Differentiate between physical and chemical changes.
Identify examples of physical changes, such as melting of wax.
Recognize indicators of chemical changes, including color and temperature variations.
Understand the process and prevention of rusting.
Explain the transformation of milk into curd as a chemical change.
Analyze the properties of iron that contribute to its stability.

Topics covered

Paper topics

Physical Changes
Chemical Changes
Characteristics of Physical Changes
Characteristics of Chemical Changes
Rusting of Iron
Prevention of Rusting
Milk to Curd Transformation
Indicators of Chemical Reactions
Reversible and Irreversible Changes
Examples of Physical Changes
Examples of Chemical Changes
Properties of Iron

Important topics

Distinguishing Physical and Chemical Changes
Indicators of Chemical Reactions
Rusting of Iron and its Prevention
Irreversible Nature of Chemical Changes
Practical Examples of Changes

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Questions and Solutions

Multiple Choice Questions

1. Which of the following is a physical change?

a) Rusting of iron

b) Combustion of magnesium ribbon

c) Burning of candle

d) Melting of wax

Solution: The correct option is (d) Melting of wax. A physical change alters the form or appearance of a substance but does not change its chemical composition. Melting wax involves a change of state from solid to liquid, but the substance remains wax. Rusting of iron, combustion of magnesium, and burning of a candle are chemical changes because they produce new substances.

2. Which of the following is a chemical change?

a) Twinkling of stars

b) Cooking of vegetables

c) Cutting of fruits

d) Boiling of water

Solution: The correct option is (b) Cooking of vegetables. Cooking involves chemical reactions that break down complex molecules in vegetables and form new substances, altering their taste, texture, and nutritional value. Twinkling of stars is an optical phenomenon, cutting fruits is a physical change (changing size and shape), and boiling water is a physical change (changing state from liquid to gas).

3. A chemical change may involve –

a) change in colour only

b) change in temperature only

c) evolution of gas only

d) any or all of the above

Solution: The correct option is (d) any or all of the above. Chemical changes are often accompanied by observable signs. These can include a change in the color of the substance, a change in temperature (either releasing heat or absorbing heat), or the release of a gas, which might be seen as bubbles or a change in smell.

4. Which of the following is/are true when milk changes into curd?

(i) Its state is changed from liquid to semi-solid.

(ii) It changes colour.

(iii) It changes taste.

(iv) The change cannot be reversed.

Choose the correct option from below:

(a) (i) and (ii) are correct

(b) (ii) and (iii) are correct

(d) (i) to (iv) are correct

Solution: The correct option is (c) (i), (iii) and (iv) are correct. When milk turns into curd, it undergoes a chemical change. Its texture changes from liquid to a semi-solid consistency. The taste becomes sour due to the formation of lactic acid. This transformation is generally irreversible; you cannot easily turn curd back into milk. While the color might slightly change, the primary indicators are the change in state, taste, and irreversibility.

5. A man painted his main gate made up of iron, to:

(i) prevent it from rusting.

(ii) protect it from sun.

(iii) make it look beautiful.

(iv) make it dust free.

Which of the above statement(s) is/are correct?

(a) (i) and (ii)

(b) (ii) and (iii)

(d) (i) and (iii)

Solution: The correct option is (d) (i) and (iii). Painting an iron gate serves two main purposes. Firstly, it creates a protective barrier that prevents moisture and air from reaching the iron surface, thus preventing rusting (a chemical change). Secondly, it enhances the aesthetic appearance of the gate. While painting might offer some minor protection from the sun and help keep dust from adhering as easily, preventing rust and improving appearance are the primary reasons.

6. Iron pillar near the Qutub Minar in Delhi is famous for the following facts. Which of these facts is responsible for its long stability?

(a) It is more than 7 metres high.

(b) It weighs about 6000 kg.

(d) It has not rusted after such a long period.

Solution: The correct option is (d) It has not rusted after such a long period. The Delhi iron pillar is a remarkable historical artifact primarily because it has resisted rusting for over 1600 years. While its height and weight are impressive, and its age is significant, the key factor contributing to its long-term stability and preservation is its unusual resistance to the chemical process of rusting, which would normally degrade iron over time.

Common mistakes

Confusing reversible physical changes with irreversible chemical changes.
Overlooking subtle indicators of chemical reactions like temperature or gas evolution.
Not recognizing that a single event can involve multiple types of changes.
Failing to identify the formation of new substances as the defining characteristic of a chemical change.

Revision tips

Focus on the key differences between physical and chemical changes, especially reversibility.
Memorize common examples provided in the solutions for both types of changes.
Pay close attention to the explanations for why certain changes are classified as chemical.
Review the conditions and prevention methods for rusting.
Use the MCQ format to test your understanding of the concepts.

Practice MCQs

Q1. Which of the following processes is considered a physical change?

Q2. Which of the following is an example of a chemical change?

Q3. A chemical change can be characterized by which of the following?

Q4. When milk transforms into curd, which of the following statements are true?

Q5. A man painted his iron gate primarily to:

Q6. The long stability of the iron pillar near the Qutub Minar is attributed to:

Frequently asked questions

What is the main difference between a physical and a chemical change?

In a physical change, the form or appearance of a substance changes, but its chemical identity remains the same (e.g., melting ice). In a chemical change, a new substance with different properties is formed (e.g., burning wood).

What are some common indicators of a chemical change?

Common indicators include a change in color, a change in temperature (heat released or absorbed), the evolution of a gas (bubbles), or the formation of a precipitate.

Why is the rusting of iron considered a chemical change?

Rusting is a chemical change because iron reacts with oxygen and moisture to form a new substance, iron oxide (rust), which has different properties than iron.

How can rusting of iron be prevented?

Rusting can be prevented by preventing iron from coming into contact with oxygen and moisture. Methods include painting, greasing, galvanizing, and alloying iron with other metals.

Is the change of milk into curd a physical or chemical change?

The change of milk into curd is a chemical change. Bacteria convert lactose (milk sugar) into lactic acid, which alters the taste, texture, and chemical composition of milk, forming a new substance.

Are all chemical changes irreversible?

Most chemical changes are irreversible, meaning the new substances formed cannot easily be converted back into the original substances. For example, you cannot easily turn ash back into wood.

How do these NCERT solutions help in exam preparation?

These solutions provide clear, step-by-step answers to typical questions on physical and chemical changes, helping students understand the concepts, identify key indicators of different changes, and practice applying this knowledge to various examples.

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