CBSE Class 6 Science Exemplar Chapter 6: Changes Around Us - NCERT Solutions

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NCERT Solutions PDF Class 6 PDF

This resource provides comprehensive NCERT Solutions for CBSE Class 6 Science Exemplar, Chapter 6, focusing on 'Changes Around Us'. It covers key concepts like reversible and irreversible changes, explaining the differences with examples such as melting and freezing of substances, burning, blooming, hardening, and the processes involved in making a chapati. The solutions clarify why certain changes can be undone while others are permanent. This chapter is crucial for understanding the physical and chemical transformations in our surroundings. These solutions are designed to help students grasp these fundamental scientific principles, prepare for exams, and build a strong foundation in science by offering clear, step-by-step explanations for each multiple-choice question, aiding in effective revision and concept reinforcement.

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Quick info

BoardCBSE
ClassClass 6
SubjectScience Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 6

Chapter summary

Chapter 6, 'Changes Around Us', in the CBSE Class 6 Science Exemplar NCERT Solutions delves into the nature of changes occurring in our environment. It distinguishes between changes that can be reversed and those that cannot. The solutions explain concepts like expansion and contraction due to heating and cooling, and the difference between physical changes (like melting and freezing) and irreversible changes (like burning). This chapter helps students identify and classify various everyday changes, fostering an understanding of basic scientific processes.

Learning outcomes

  • Understand the difference between reversible and irreversible changes.
  • Identify examples of reversible changes in everyday life.
  • Identify examples of irreversible changes in everyday life.
  • Explain how heating and cooling can cause changes.
  • Differentiate between physical changes and permanent changes.
  • Analyze observed changes and classify them.

Topics covered

Paper topics

  • Changes Around Us
  • Reversible Changes
  • Irreversible Changes
  • Melting
  • Freezing
  • Burning
  • Blooming
  • Hardening of Cement
  • Expansion on Heating
  • Contraction on Cooling
  • Physical Changes
  • Separation by Evaporation

Important topics

  • Distinguishing Reversible and Irreversible Changes
  • Examples of Reversible Changes
  • Examples of Irreversible Changes
  • Effect of Heat on Materials
  • Physical vs. Permanent Changes

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Questions and Solutions

Multiple Choice Questions:

1. Pick the change that can be reversed from the following. (a) Cutting of trees (b) Melting of ghee (c) Burning of candle (d) Blooming of flower
Solution:

(b) Melting of ghee

The change where ghee melts is reversible because the liquid ghee can be cooled down to solidify again. In contrast, cutting trees, burning a candle, and a flower blooming are irreversible changes; they cannot be undone to return to their original state.

2. Which of the following change cannot be reversed? (a) Hardening of cement (b) Freezing of ice cream (c) Opening a door (d) Melting of chocolate
Solution:

(a) Hardening of cement

The hardening of cement is an irreversible change. Once cement mixes with water and hardens, it undergoes a chemical reaction and cannot be reverted to its original liquid or powder form.

3. An iron ring is heated. Which of the following statement about it is incorrect? (a) The ring expands. (b) The ring almost comes to the same size on cooling. (c) The change in this case is reversed. (d) The ring changes its shape and the change cannot be reversed.
Solution:

(d) The ring changes its shape and the change cannot be reversed.

When an iron ring is heated, it expands. Upon cooling, it contracts and returns to nearly its original size. This indicates that the change is reversible. Therefore, the statement that the change cannot be reversed is incorrect.

4. While lighting a candle, Paheli observed the following changes. (i) Wax was melting (ii) Candle was burning (iii) Size of the candle was reducing (iv) Melted wax was getting solidified Of the above, the changes that can be reversed are (a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (d) (i) and (iv)
Solution:

(d) (i) and (iv): Wax was melting; Melted wax was getting solidified

The melting of wax (i) is a reversible change because the liquid wax can cool down and solidify again. Similarly, the solidification of melted wax (iv) is also a reversible process. The burning of the candle (ii) and the reduction in its size (iii) are irreversible changes as the wax is converted into gases and ash.

5. Salt can be separated from its solution (salt dissolved in water), because (a) mixing of salt in water is a change that can be reversed by heating and melting of salt (b) mixing of salt in water is a change that cannot be reversed (c) mixing of salt in water is a permanent change (d) mixing of salt in water is a change that can be reversed by evaporation
Solution:

(d) mixing of salt in water is a change that can be reversed by evaporation.

When salt dissolves in water, it forms a solution. This process is reversible because evaporating the water leaves the solid salt behind. The water can also be collected and condensed, and the salt can be re-dissolved, demonstrating the reversibility of the change.

6. Rolling of chapati and baking of chapati are the changes that (a) can be reversed (b) cannot be reversed (c) can be reversed and cannot be reversed, respectively (d) cannot be reversed and can be reversed, respectively
Solution:

(c) can be reversed and cannot be reversed, respectively.

Rolling the dough into a flat chapati is a physical change that can be reversed by reshaping it. However, baking the chapati involves cooking, which causes chemical changes, making it an irreversible process. The baked chapati cannot be turned back into raw dough.

7. Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim (a) expands and fits onto the wooden wheel (b) contracts and fits onto the wooden wheel (c) no change in the size takes place (d) expands first, then on cooling contracts and fits onto the wooden wheel.
Solution:

(d) expands first, then on cooling contracts and fits onto the wooden wheel.

When the iron rim is heated, it expands in size. This expansion allows it to be easily placed over the wooden wheel. As the rim cools down, it contracts, gripping the wooden wheel tightly and securing it in place. This process utilizes the principle of thermal expansion and contraction.

Common mistakes

  • Confusing reversible physical changes with irreversible chemical changes.
  • Assuming all changes involving heat are irreversible.
  • Not recognizing that some seemingly permanent changes can be reversed under specific conditions.
  • Misclassifying changes like burning or blooming as reversible.

Revision tips

  • Focus on understanding the core difference between reversible and irreversible changes.
  • Create a list of examples for each type of change encountered in daily life.
  • Pay close attention to the reasoning provided for each solution, especially for the MCQ options.
  • Review the examples of heating and cooling effects on materials like iron and wax.

Practice MCQs

Q1. Which of the following changes is considered reversible?

Q2. Identify the change that cannot be reversed.

Q3. When an iron ring is heated, it expands. What happens upon cooling?

Q4. In the process of lighting a candle, which changes are reversible?

Q5. Salt dissolved in water can be separated by evaporation because:

Q6. Rolling of chapati vs. baking of chapati - which statement is correct?

Q7. An iron rim is heated to fit onto a wooden wheel. Why?

Frequently asked questions

What are the main types of changes discussed in Chapter 6 of CBSE Class 6 Science Exemplar?

Chapter 6 discusses two main types of changes: reversible changes, which can be undone, and irreversible changes, which cannot be undone.

Can you give an example of a reversible change from the chapter?

Yes, melting of ghee is a reversible change. The melted ghee can be cooled to become solid again.

What is an example of an irreversible change mentioned in the solutions?

The hardening of cement is an example of an irreversible change, as it cannot be returned to its original liquid state.

How does heating affect an iron ring according to the solutions?

According to the solutions, an iron ring expands when heated and contracts back to its original size when cooled, demonstrating a reversible change.

How can salt be separated from its solution?

Salt can be separated from its solution by evaporating the water. This is because dissolving salt in water is a reversible change.

Are rolling and baking a chapati the same type of change?

No, rolling a chapati is a reversible change, while baking a chapati is an irreversible change because it alters the dough permanently.

Important links

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