# CBSE NCERT Solutions for Class 6 Science Chapter 5

NCERT Solutions of chapter 5 for class-6 are given below. In the explanation of chapter 5 of class 6 science, historical facts about chapters, main points of the chapter, assignments, chapter test, previous years questions, etc are given.

Important questions based on NCERT syllabus for Chapter 1 - Knowing our Numbers:

Question-1:

Given examples to explain the difference between changes that can or cannot be
reversed.

Solution:

To explain the differences between changes that can or cannot be reversed, some
examples are given below.

1. If we inflate a balloon, the size and shape of the balloon undergoes a change. However, the original size and shape of the balloon can be obtained back by allowing the air to escape from the balloon. This means that the change that occurs by inflating a balloon can be reversed. But, if the balloon bursts after being inflated, then its original size and shape cannot be obtained back. Thus, in this case, the change cannot be reversed.
2. If we fold a piece of paper, then the shape and size of the paper undergoes a change. In this case, the original shape and size of the original paper can be obtained back. Thus, change can be reversed. However, if we cut the piece of paper, the change in the shape and size of the paper cannot be reversed.
3. After we roll out a chapatti from a ball of dough, the chapatti can be converted back into a ball. Thus, the change occurring here can be reversed. But, if we cook the chapatti on a tawa, then it cannot be converted back into a ball of dough. Thus the change is irreversible.

Question-2:

A thick coating of plaster of paris (POP) paste is applied over the bandage on a
fractured bone. It became hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed?

Solution:

When water is added to plaster of paris (POP), it changes to another substance
and on drying it hardens. Once the POP has hardened, its shape cannot be changed.
Therefore, the change in POP cannot be reversed.

Question-3:

A bag of cement lying in the open gets wet due to rain during the night. The
next day, the sun shines brightly. Do you think the changes that have occurred in the cement can be reversed?

*Solution: In this case, the changes cannot be reversed. This is because the cement that hardens up after getting wet cannot be obtained back.