Question: 58. On heating, some solid substances change from solid to vapour state without passing through liquid state. The technique used for the purification of such solid substances based on the above principle is known as :
(1) Crystallization
(2) Sublimation
(3) Distillation
(4) Chromatography
Answer: Option (2)
Explanation:
Sublimation is the process in which a substance directly changes from solid state to vapour state without passing through the liquid state.
Some solid substances like camphor, naphthalene and ammonium chloride show this property on heating.
In the purification technique based on this principle, the impure solid is heated and the vapours formed are cooled to obtain the pure solid directly.
Crystallization is used to purify solids based on differences in solubility.
Distillation is used for purification of liquids based on differences in boiling points.
Chromatography is used to separate components of a mixture based on differential adsorption or partition.
Therefore, the correct technique is sublimation and the correct answer is Option (2).