NCERT Class VI Science Solutions: Chapter 6 – Changes around Us Part 3

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Question 12:

Which of the following changes cannot be reversed.

  1. Blowing of a balloon.

  2. Folding a paper to make a toy aero plane.

  3. Rolling a ball of dough to make roti.

  4. Baking cake in an oven.

  5. Drying a wet cloth.

  6. Making biogas from cow dung.

  7. Burning of a candle.

Answer:

(D), (F) and (G)

Question 13:

Boojho’s sister broke a white dove, a symbol of peace, made of Plaster of Paris (POP). Boojho tried to reconstruct the toy by making a powder of the broken pieces and then making a paste by mixing water. Will he be successful in his effort? Justify your answer.

Answer:

Boojho will not be successful, because making of toy from Plaster of Paris (POP) is a change that cannot be reversed.

Question 14:

Tearing of paper is said to be a change that cannot be reversed. What about paper recycling?

Answer:

We do get the paper on paper recycling but it is not the same original paper that we get. The colour and texture of the paper changes.

LONG ANSWER QUESTIONS

Question 15:

Give one example in each case

  1. Change which occurs on heating but can be reversed.

  2. Change which occurs on heating but cannot be reversed.

  3. Change which occurs on cooling but can be reversed.

  4. Change which occurs on mixing two substances, but can be reversed.

  5. Change which occurs on mixing two substances, but cannot be reversed.

Answer:

  1. Heating of an iron rod.

  2. Baking of chapati.

  3. Formation of Ice from water.

  4. Formation of salt solution.

  5. Mixing of cement and water.

Question 16:

A potter working on his wheel shaped a lump of clay into a pot. He then baked the pot in an oven. Do these two acts lead to the same kind of changes or different? Give your opinion and justify your answer.

Answer:

Hint: Different kinds: former can he reversed while the later cannot be reversed.

Question 17:

Conversion of ice into water and water into ice is an example of change which can be reversed. Give four more examples where you can say that the changes can be reversed.

Answer:

  1. Melting of wax

    Image of melting wax

    Image of Melting Wax

    Image of melting wax

  2. Folding of a paper

  3. Knitting of a sweater

    Image of Knitting of a sweater

    Image of Knitting of a Sweater

    Image of Knitting of a sweater

  4. Inflating of a tire