JEE Main 2025 · 28 January · evening · Single correct · +4 / −1
The purification method based on the following physical transformation is :
Solid →(Heat) Vapour →(Cool) Solid
- (a) Extraction
- (b) Crystallization
- (c) Distillation
- (d) Sublimation
Answer and solution
Answer (d) Sublimation
Solution
Chemistry ma’am · 4 steps
Look at what the solid skips: it goes straight to vapour and back, with no liquid in between.
- Read the change. On heating, solid X turns directly into vapour. On cooling, that vapour turns directly back into solid X. No liquid stage appears anywhere.
- Name the process. A solid changing straight into vapour without melting is called sublimation. Substances like camphor, naphthalene, iodine and anthracene behave this way.
- Why it purifies. The sublimable compound leaves as vapour and collects as pure solid on a cool surface. The non-sublimable impurities stay behind.
- So. The method is sublimation, option (d).
The idea to keep. Track the states. Solid to vapour to solid is sublimation, liquid to vapour to liquid is distillation, and a solution giving crystals is crystallization.
Answer from the NTA final answer key. Solution by PrepWiser.