Science [1 Marks Each] QUE - ANS

No, because it is an irreversible change.

A change may occur by heating a substance or by mixing it with some other.

No, because once the idli batter is steamed, it undergoes a chemical change which is irreversible.

Reversible change.

No. This change cannot be reversed.

Conversion of water into water vapour is a reversible change because water vapour when cooled gets converted into liquid water again.

No, deforestation can’t be considered as a reversible change because no same tree can be planted after felling down or cutting.

It turns into ash. It is not a reversible change.

No.

Yes.

Explosion of crackers is a chemical change because the explosive reactants are transformed into gaseous products along with heat and light and thus cannot be reversed.
Hence, it is a chemical change.

This is a change which cannot be reversed.

We can reverse this change by evaporation of water by which salt can be obtained. Water vapours are condensed to get liquid water.

Ring of iron blade heated before fixing it into handle of a tool because on heating ring becomes slightly larger in size, therefore it expand and handle fits easily into it.

Yes.

During the process of rusting, the iron has to be in contact with the moist air or water.

An iron expands and becomes soft on heating. Then it can be changed into desired shape.

This happens because the heat energy required for the change is provided by the body.

No.

Yes.

No.

No.

The quantity of water in a pan decreases when we keeps on heating it because water changes into its vapour.

Yes.

Match stick changes into ash and this is a change that cannot be reversed.

Formation of clouds is a physical change as it is phase transformation cycle of natural water from liquid to gas and then, gas to liquid. Hence, the property of water never changes in clouds form.

Reversible changes: Melting of wax and stretching of a rubber band.
Irreversible changes: Burning of a paper and growth of plants.

When we keep on heating water in a pan, the quantity of water in the pan decreases.

If we take some wax in a pan and heat it, this change can be reversed.

This is a change which cannot be reversed.

When we bum a piece of paper, it changes into ash and smoke. We cannot combine the ash and smoke to form the original piece of paper. So the burning of a piece of paper is an irreversible change.

Yes.

The shape and size of balloon can be changed by blowing it.

No.

Printing is an irreversible change because we cannot separate and collect the printing ink after printing.

When sugar is continuously heated in the porcelain dish, it becomes foggy due to water vapour. A black powdery substance is left behind, which is charcoal. This process is also called charring of sugar and this is a chemical change.

No.

This is a reversible change.

Yes. The length of the dress can again be increased by unfolding it. Hence, this change can be reversed.

Melting of ice is a reversible change because on melting ice changes into water but the water can again be freezed to change it into ice.

Fast changes take place over a short duration of time.
Slow changes take a longer duration of time to complete.

• Heating or cooling
• Mixing two or more substances
• By applying force etc.

Ironing removes the wrinkles of the clothes, which can come back in the same condition. Hence, ironing of a cloth is a reversible change.

Yes.

No, because one material influences the other. For example, sharpening of a pencil with blade.