The azeotropic mixture of water and ethanol boils at 78.15°C. When this mixture is distilled, it is possible to obtain:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Neither H2O nor C2H5OH in the pure state
An azeotrope boils at a constant temperature with the same composition in the liquid and the vapour, so on distillation the distillate is again the azeotrope and no further separation occurs.
Why the other options are incorrect
Option (1) Pure H2O — Incorrect. Water cannot be drawn off on its own, because the vapour carries both components in the azeotrope ratio.
Option (2) Pure C2H5OH — Incorrect. For the same reason, distillation stops at about 95% ethanol; it does not give pure ethanol.
Option (3) Pure H2O as well as pure C2H5OH — Incorrect. Neither component can be separated, so both cannot be obtained either.
NCERT (2026-27 edition):
1.5.2 Non-ideal Solutions – “Some liquids on mixing, form azeotropes which are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature. In such cases, it is not possible to separate the components by fractional distillation. … For example, ethanol-water mixture (obtained by fermentation of sugars) on fractional distillation gives a solution containing approximately 95% by volume of ethanol. Once this composition, known as azeotrope composition, has been achieved, the liquid and vapour have the same composition, and no further separation occurs.”