The solution which shows positive deviation from Raoult's law, is the mixture of
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Ethanol and acetone
A solution shows positive deviation from Raoult's law when the A–B attractions are weaker than the A–A and B–B attractions in the pure liquids. Molecules escape more easily, so the vapour pressure is higher than Raoult's law predicts; mixing absorbs heat (\( \Delta_{mix}H \gt 0 \)) and the volume increases (\( \Delta_{mix}V \gt 0 \)). In negative deviation the A–B attractions are stronger and everything is reversed.
Ethanol and acetone fit the first case: acetone weakens the hydrogen bonding between ethanol molecules, so the A–B attractions are weaker and the solution shows positive deviation.
Why the other options are incorrect
Option (1) Nitric acid and water — Incorrect. Nitric acid and water attract each other strongly, so the A–B attractions are stronger than in the pure liquids and the solution shows negative deviation. It forms a maximum boiling azeotrope (about 68% nitric acid by mass, boiling point 393.5 K).
Option (3) Phenol and Aniline — Incorrect. These show negative deviation: the –OH hydrogen of phenol forms a hydrogen bond with the nitrogen of aniline, which is stronger than the attractions between like molecules, so the vapour pressure falls.
Option (4) Chloroform and Acetone — Incorrect. These show negative deviation: the hydrogen of chloroform forms a hydrogen bond with the oxygen of acetone, \( \ce{O=C(CH3)2} \), so the A–B attraction is stronger and the vapour pressure falls.
NCERT (2026-27 edition):
Non-ideal Solutions – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 29-05 S1 | – | 22-06 S3 | – |