The chalk keeps breaking into smaller and smaller pieces, and at no stage does it stop being chalk. The stick snaps into two clean pieces (Fig. 7.1b), and those pieces snap again — until the bits are so small that your fingers can no longer grip them and break them. The mortar and pestle take over where your hands stop. Grinding turns those bits into a fine white powder (Fig. 7.1c). Under a magnifying glass (Fig. 7.1d) the powder is not a smooth paste at all — it is a very large number of separate tiny grains , each one white and chalky. What this tells us: the stick of chalk was never a single continuous block of material. It was a huge number of small units packed together, and breaking it merely separates them. Grinding harder would only make the specks finer still.

NCERT Solutions Curiosity Chapter 7 Activity 7.1: Let us explore — What Is Matter Composed of?

Book page 99 Updated on2026-09-05

Q1.

What do you observe?

Answer

The chalk keeps breaking into smaller and smaller pieces, and at no stage does it stop being chalk.

The stick snaps into two clean pieces (Fig. 7.1b), and those pieces snap again — until the bits are so small that your fingers can no longer grip them and break them.
The mortar and pestle take over where your hands stop. Grinding turns those bits into a fine white powder (Fig. 7.1c).
Under a magnifying glass (Fig. 7.1d) the powder is not a smooth paste at all — it is a very large number of separate tiny grains, each one white and chalky.

What this tells us: the stick of chalk was never a single continuous block of material. It was a huge number of small units packed together, and breaking it merely separates them. Grinding harder would only make the specks finer still.

Q2.

Each tiny grain you observe is still a speck of chalk.

Answer

Yes — and the magnifying glass is what lets you check it for yourself. Every grain in the powder has the same white colour, the same dusty feel and the same chalky nature as the original stick.

This single observation carries the whole idea of the section. If breaking chalk had produced something else, the powder would look and behave differently. It does not. So a piece of chalk must be made up of a large number of identical units, and breaking simply pulls those units apart from one another.

Try this: rub a little of the powder on a blackboard. It still writes. A substance keeps its properties right down to the smallest speck you can make of it — which is the first thing the particle model claims.

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