Step-by-step explanation

We need to decide which of the listed objects are in random motion.

Random motion means motion that is irregular and unpredictable in direction because of constant collisions with surrounding particles.

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I. Pollen grains in water

Pollen grains suspended in water show Brownian motion.

This happens because the tiny pollen grains are constantly hit by water molecules moving in different directions. Since the collisions are uneven, the pollen grains move in a zig-zag, random path.

So, statement I is correct.

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II. The molecules of hydrogen gas

Gas molecules are always moving randomly.

In a gas, molecules move freely in all directions and collide with one another and with the walls of the container. Their motion is random because their speeds and directions keep changing after collisions.

So, statement II is correct.

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III. Fine chalk particles floating in air

Fine chalk particles floating in air also show random motion.

They are small enough to be constantly struck by air molecules from different directions. These uneven collisions cause the chalk particles to move irregularly, similar to Brownian motion.

So, statement III is correct.

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Therefore, all three are in random motion:

$$\text{I, II and III}$$

The correct answer is:

(D) I, II and III.