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NCERT Solutions Curiosity Chapter 7 In-text Questions — What Is Matter Composed of?

Book page 100 Updated on2026-09-05

Q1.
Are the units of chalk obtained in this manner considered the smallest units of chalk?
Answer

Not the units in your mortar — but yes, the units the process finally leads to. The two must be kept apart.

  • What the mortar and pestle actually give you is very fine chalk powder. Every speck of it is still made of millions and millions of constituent particles. It is nowhere near the smallest unit.
  • The text asks you to imagine the grinding continuing. Eventually a stage would come at which the pieces cannot be broken down any further. Those tiny units are the basic building blocks the chalk was made of — its constituent particles.
Why the imagining is needed: no mortar can actually reach that stage, and the particles are far too small to be seen even through an ordinary microscope. We reach the idea by reasoning from what we can see — that every speck, however fine, is still chalk.
What the model does not claim here: the chapter does not say these units can never be divided by any means at all. It says they are the smallest units of chalk — split them and you no longer have chalk. What they are made of comes in higher grades (see A step further, page 115: atoms and molecules).
Q2.
Recall the dissolution of sugar into water to form a solution. What happens to sugar when it is dissolved in water?
Answer

The sugar breaks up into its constituent particles, which separate from one another and spread out into the spaces between the water particles.

Each tiny grain of sugar is made up of millions and millions of such particles. Water pulls them out of the grain one by one and they slip into the interparticle spaces that already exist in the water. Because those particles are extremely small and now spread singly through the liquid, no grain of sugar can be seen any more.

The sugar has not disappeared and it has not been destroyed. Every spoonful of the solution tastes sweet, so the sugar particles must be everywhere in it.

Q3.
Do you observe any sugar particles in the solution?
Answer

No — not a single one, anywhere in the tumbler.

There are two reasons together, and both matter:

  1. The constituent particles of sugar are extremely small — so small that they cannot be seen even through an ordinary microscope, let alone the naked eye.
  2. They are no longer packed together in a grain. Each one has moved off separately into the interparticle spaces of the water, so there is nothing left that is big enough to see.
But they are still there: the water tastes sweet at the top layer as well as at the bottom. Taste is the evidence that seeing cannot give. Not being able to see a thing is not proof that it is absent — a point worth remembering every time this chapter talks about invisible particles.
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