The vapour pressure of pure solvent is 0.8 mm of Hg at a particular temperature. On addition of a non-volatile solute ‘A’ the vapour pressure of solution becomes 0.6 mm of Hg. The mole fraction of component ‘A’ is

According to Raoult's law, the lowering in vapour pressure is written as, 0 2 0 P P X P We are provided with the following data: Vapour pressure of the pure solvent is 0P 0.8 mm of Hg Vapour pressure of solvent on the addition of solute is P 0.6 mm of Hg Let's substitute the values in the equation. We have, 2 2 0.8 0.6 X 0.8 X 0.25 >> Thus, (a) is the correct option.