P_{solution} ∝ x_{A} by Raoult’s law. where x_{A} is the mole fraction of the solvent.

P_{solution} = k . x_{A}

When

x_{A} = 1

k = P^{0}_{Solvent}

P^{0}_{Solvent} = partial pressure of pure solvent

P_{solution} = P^{0}_{solvent} . x_{A}

where

x_{B} = mole fraction of the solute

x_{A} + x_{B} = 1

x_{B} = 1 – x_{A}