Which of the following methods is best suited for the separation of a mixture containing naphthalene and benzoic acid

The correct option is Sublimation.

Let us understand the step-by-step reasoning for why sublimation is the best method to separate a mixture of naphthalene and benzoic acid:

1. Understanding the Properties of the Components:
Naphthalene is a volatile organic compound that undergoes sublimation, meaning it directly transitions from a solid state to a gaseous state upon heating without passing through the liquid state.
Benzoic acid, on the other hand, does not readily sublime at the same temperature conditions and can be separated effectively.

2. The Process of Sublimation:
When the mixture containing naphthalene and benzoic acid is heated, naphthalene sublimes and turns into vapors.
These vapors can be cooled on a cold surface to deposit back as pure solid naphthalene, leaving behind benzoic acid in the heating vessel.

3. Why Other Methods are Less Suitable:
- Crystallisation: Although both are soluble in organic solvents, separating them cleanly using simple crystallization can be difficult and less efficient compared to sublimation.
- Distillation: Distillation is used for separating liquids with different boiling points, not solid-solid mixtures where one component sublimes.
- Chromatography: While chromatography can separate them, it is a complex, analytical, and expensive technique, whereas sublimation is a straightforward, cost-effective physical separation method suitable for this mixture.