Azeotropes are binary mixtures having

The correct answer is Option (1) → Same composition in liquid and vapor phase, constant boiling temperature and they cannot be separated by fractional distillation.

Fractional distillation separates two liquids only because the vapour is richer in the more volatile one. In an azeotrope the liquid and the vapour have the same composition, so distillation cannot change it and the mixture cannot be separated by fractional distillation.

A large positive deviation gives a minimum boiling azeotrope (ethanol–water, about 95% ethanol by volume); a large negative deviation gives a maximum boiling azeotrope (nitric acid–water, about 68% nitric acid by mass).

Why the other options are incorrect

• Option (2) The same composition in the liquid and vapor phase, constant boiling temperature and they can be separated by distillation. — Incorrect. Because the vapour has the same composition as the liquid, distillation does not separate an azeotrope.

• Option (3) The same composition in the liquid and vapor phase, constant boiling temperature, they cannot be separated by fractional distillation and have equal volume of the two liquids. — Incorrect. The first three parts are right, but the azeotropic composition is fixed by the pair of liquids and is not equal volumes (ethanol–water is about 95 : 5).

• Option (4) Constant boiling temperature, they can be separated by fractional distillation and have equal volumes of two liquids. — Incorrect. Both added parts are wrong: azeotropes cannot be separated by fractional distillation, and their composition is not equal volumes.

NCERT (2026-27 edition):
Non-ideal Solutions – …