Statement I: When an ideal binary solution of liquids A and B is distilled, the boiling point of the distillate is lower than that of the original solution.
Statement II: When an ideal binary solution of liquids A and B is distilled, the distillate contains a larger proportion of the more volatile liquid.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.
In an ideal solution of two volatile liquids, the more volatile liquid has the higher vapour pressure and the lower boiling point. On distillation, the vapour is collected and condensed as the distillate.
Statement I: When an ideal binary solution of liquids A and B is distilled, the boiling point of the distillate is lower than that of the original solution. — True. A liquid boils when its vapour pressure equals the atmospheric pressure. The distillate has a higher vapour pressure than the original solution, so it reaches the atmospheric pressure at a lower temperature.
Statement II: When an ideal binary solution of liquids A and B is distilled, the distillate contains a larger proportion of the more volatile liquid. — True. At equilibrium the vapour phase is richer in the more volatile component than the liquid, and the distillate is this condensed vapour.
Why Statement II explains Statement I? By Raoult’s law, the total vapour pressure of an ideal solution rises as the mole fraction of the more volatile liquid rises. The distillate is richer in that liquid, so its vapour pressure is higher and it boils below the boiling point of the original solution.
NCERT (2026-27 edition):
1.4.1 Vapour Pressure of Liquid-Liquid Solutions – “… it may thus be concluded that at equilibrium, vapour phase will be always rich in the component which is more volatile.”
1.6.2 Elevation of Boiling Point – “The vapour pressure of a liquid increases with increase of temperature. It boils at the temperature at which its vapour pressure is equal to the atmospheric pressure.”