NCERT Solutions Curiosity Chapter 8 Chapter opening — In-text Questions

Book page 143 Updated on2026-09-05

Q1.

Aavi has a counterview to Thirav. What do you think? Why?

Answer

Aavi is right. Ice and water are not two different substances — they are the same substance in two different states.

Thirav's reason was that ice feels hard and can be held in the hand, while water cannot. That is a real difference, but it is a difference of state, not of substance.

What Thirav noticed	What it actually shows
Ice is hard and keeps its shape	In the solid state the particles are locked in fixed places
Water cannot be held in the hand	In the liquid state the particles can slide over one another, so water flows away
Same substance?	Yes — nothing was added or removed, only heat

Why we can be sure: the change works both ways. Keep water in a freezer and you get ice; take the ice out and it melts back into exactly the same water. If ice were a different substance, melting it would not give the water back. Also, the ice cube in the shikanji does not make the drink more or less than it was — it simply melts into it.

Check it yourself: Weigh a closed bottle with 100 g of water. Freeze it and weigh again. The reading does not change — the ice is that very same water.

Q2.

Do you think Thirav is right? How can you find out?

Answer

No, Thirav is not right. He thinks that when water is kept in a freezer, something gets added to it and that is why ice is formed. Nothing is added — the water only loses heat and freezes.

How to find out — a simple test you can do at home:

Take a small bottle and fill it with drinking water. Mark the level and note the mass on a kitchen balance.
Close the lid tightly and keep the bottle in the freezer for a few hours, until the water becomes ice.
Take it out and weigh it again — the mass is the same. Nothing has entered the closed bottle.
Leave the bottle on the table. The ice melts back into water, and the water is as clear and tasteless as before.

Why this settles the question: if something had been added inside the freezer, (a) the mass would have increased, and (b) the melted water would be different in some way — cloudy, salty, or larger in amount. Neither happens. The only thing that changed was the temperature: the water was cooled to 0 °C and below, so it froze.

Did you know? Water is unusual — it expands a little on freezing. That is why a full bottle of water sometimes cracks or bulges in the freezer. The amount of water is still the same; only the space it takes up has increased.

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