At equilibrium, the vapour phase above a liquid solution is always richer in the component that:
AIs more volatile (higher pure-component vapour pressure)
BHas the lower mole fraction in liquid
CHas the higher molar mass
DIs less volatile
Answer & Solution
Correct answer: A. Is more volatile (higher pure-component vapour pressure)
The more volatile component has higher p⁰, contributes more to vapour pressure, and the vapour is therefore **enriched in the more volatile component** — the basis of fractional distillation.
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