NCERT Solutions Curiosity Chapter 7 Activity 7.8: Let us experiment — How Particles Move in Different States of Matter?
Book page 109 Updated on2026-09-05
Q1.
What do you observe?
Answer
The colour travels through the water on its own, without any stirring.
At first — thin streaks of pink spread out from the grain of potassium permanganate at the bottom, reaching upwards and sideways (Fig. 7.13a).
After some time — the streaks blur into one another and the entire bulk of water takes on a uniform pink colour (Fig. 7.13b).
Safety first: do not touch potassium permanganate with your hands. Use a spoon or a spatula to handle it.
Q2.
Do you know why this happens?
Answer
Because the water particles are in constant motion. They do the work in two steps:
The moving water particles pull the particles of potassium permanganate out of the grain, one after another.
They then keep hitting those freed particles, knocking them this way and that until they are spread throughout the liquid.
Nothing is stirred and nothing is poured. The spreading is done entirely by particles that are moving anyway, all the time, whether you are watching or not.
Why sand behaves differently: in many substances the constituent particles are held together so strongly that the water particles are unable to pull them out at all. Such substances — sand is the example the book gives — are insoluble in water. Step 1 fails, so step 2 never begins.