A binary ideal solution of AB type has:

The correct answer is Option (2) → ΔH_mix = 0, ΔV_mix = 0

An ideal solution obeys Raoult’s law over the entire range of concentration. In it the A–B attractions are nearly equal to the A–A and B–B attractions. So mixing the components:

• releases or absorbs no heat: Δ_mixH = 0

• causes no change in volume: Δ_mixV = 0

Examples are n-hexane + n-heptane and bromoethane + chloroethane.

Why the other options are incorrect

• Option (1) ΔH_mix = 0, ΔV_mix ≠ 0 — Incorrect. A change in volume on mixing means the intermolecular attractions have changed, which is a property of a non-ideal solution.

• Option (3) ΔH_mix ≠ 0, ΔV_mix ≠ 0 — Incorrect. Both changes are non-zero only for non-ideal solutions, such as ethanol + acetone (positive deviation).

• Option (4) ΔH_mix ≠ 0, ΔV_mix = 0 — Incorrect. Heat change on mixing also shows that the A–B attractions differ from A–A and B–B, so the solution is not ideal.

NCERT (2026-27 edition):
Ideal Solutions