JEE Chemistry 2025 Question with Solution

Given: The physical transformation is

$$\text{Solid} \xrightarrow{\text{Heat}} \text{Vapour} \xrightarrow{\text{Cool}} \text{Solid}$$

Find: The purification method represented by this transformation.

A substance that changes directly from solid to vapour on heating and directly back from vapour to solid on cooling undergoes sublimation.

This method is used to purify solids that pass directly between the solid and gaseous states without forming a liquid. Therefore, the purification method is Sublimation.

The correct option is B.

Given: The transformation shown is

$$\text{Solid} \xrightarrow{\text{Heat}} \text{Vapour} \xrightarrow{\text{Cool}} \text{Solid}$$

Find: Which purification method follows this sequence.

1. On heating, the substance changes from solid directly to vapour.
2. On cooling, the vapour changes directly back to solid.
3. Since the liquid phase is skipped in both directions, the process is called sublimation.
4. This purification method is used for substances such as iodine, camphor, naphthalene, and ammonium chloride.

Therefore, the correct answer is Sublimation, so the correct option is B.