CHANGES AROUND US

Pick the change that can be reversed from the following.

• Cutting of trees

• Melting of ghee

• Burning of candle

• Blooming of flower

Which of the following change cannot be reversed?

• Hardening of cement

• Freezing of ice cream

• Opening a door

• Melting of chocolate

An iron ring is heated. Which of the following statement about it is incorrect?

• The ring changes its shape.

• The ring almost comes to the same size on cooling.

• The change, in this case, is reversed.

• The ring expands and the change cannot be reversed.

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

• (i) and (ii)

• (ii) and (iii)

• (iii) and (iv)

• (i) and (iv)

Salt can be separated from its solution (salt dissolved in water), because

• mixing of salt in water is a change that can be reversed by heating and melting salt

• mixing of salt in water is a change that cannot be reversed

• mixing of salt in water is a permanent ‘ change

• mixing of salt in water is a change that can be reversed by evaporation.

Rolling of chapati and baking of chapati are the changes that

• can be reversed

• cannot be reversed

• can be reversed and cannot be reversed, respectively

• cannot be reversed and can be reversed, respectively.

The 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

• expands and fits onto the wooden wheel

• contracts and fits onto the wooden wheel

• contracts and fits onto the wooden wheel

• expands first, then on cooling contracts and fits onto the wooden wheel.

Which option correctly classifies the changes as reversible and irreversible?

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A student learns that the bending of metallic wire is a reversible change. Why is it considered as a reversible change?

• Because it can be changed back into its previous shape

• Because the change caused to the metallic wire is permanent

• Because the change in colour is always considered as a reversible change

• Because metallic wire changes its material more easily

A girl is making chapati. She did the following steps:

Step 1: She added water, salt, and flour to make a dough.

Step 2: She used a rolling pin to shape the dough.

Which of these options correctly explains the changes?

• Both the steps represent a reversible change

• Both the steps represent an irreversible change

• Step 1 is a reversible change and step 2 is an irreversible change

• Step 2 is a reversible change and step 1 is an irreversible change