The steam distillation method is used for the separation of 1 : 1 mixture of p-nitrophenol and o-nitrophenols because

p-nitrophenol forms an inter-molecular H-bond with the nitro group of the other molecules and o-nitrophenol forms an intramolecular H-bond with the nitro group of the same molecule.

The correct answer is Option (3) → p-nitrophenol forms an inter-molecular H-bond with the nitro group of the other molecules and o-nitrophenol forms an intramolecular H-bond with the nitro group of the same molecule.

Core Concept:

Intramolecular hydrogen bonding reduces intermolecular attraction, increases volatility, and allows steam distillation separation.

Option 1

Incorrect because o-nitrophenol has –OH and –NOâ‚‚ groups positioned ortho to each other, allowing hydrogen bonding within the same molecule (intramolecular), not between different molecules.

Option 2

Incorrect because p-nitrophenol has –OH and –NOâ‚‚ groups positioned para to each other, which are too far apart to form intramolecular hydrogen bonding.

Option 3

Correct because in o-nitrophenol, the close proximity of –OH and –NOâ‚‚ groups enables intramolecular hydrogen bonding, which reduces intermolecular interactions and increases volatility, making it steam volatile. In contrast, p-nitrophenol forms intermolecular hydrogen bonding due to larger separation between groups, leading to stronger intermolecular attraction and lower volatility.

Option 4

Incorrect because o-nitrophenol primarily forms intramolecular hydrogen bonding, not intermolecular.