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NEET levelSingle correct optionDifficulty 1 of 3so115

For a dilute solution of a non-volatile, non-electrolyte solute, the relative lowering of vapour pressure $\frac{P ^{0} - P}{P ^{0}}$ is equal to

Athe mole fraction of the solvent
Bthe mole fraction of the solute
Cthe molarity of the solute
Dthe mass fraction of the solvent

Answer: B

By Raoult's law

P = x_{1} P^{0}

, so

(P^{0} - P) / P^{0} = 1 - x_{1} = x_{2}

. The relative lowering therefore equals the mole fraction of the solute. It is not the mole fraction of the solvent, which equals

P / P^{0}

.

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