In a solution, the vapor pressure of a solvent is proportional to its mole fraction.

• A. Raoult's Law
• B. Henry's Law
• C. Freezing Point Depression
• D. Normality

Answer: (A)

Raoult's law explains this. In an ideal solution, the partial vapor pressure of a solvent equals its mole fraction in the liquid times the vapor pressure of the pure solvent at that temperature: P_solvent = X_solvent × P°_solvent. So the more solvent there is, the higher its vapor pressure; when a nonvolatile solute is added, the solvent’s mole fraction drops, and the solvent vapor pressure decreases proportionally. This linear relation holds best for ideal solutions and moderate concentrations; real solutions can show deviations if interactions between solute and solvent are strong or at higher concentrations. Henry's law, freezing point depression, and normality describe different concepts and do not capture this direct relationship between a component’s vapor pressure and its mole fraction in the liquid.