Statement I: If a liquid solute is added to a solvent which is more volatile than solvent, then vapour pressure of solution may increase, that is, \(P_s > P^o\).

Statement II: In the presence of a more volatile liquid solute, only the solute will form the vapours and solvent will not.

Statement I is correct but Statement II is false

The answer is option 3. Statement I is correct but Statement II is false.

Let us analyze each statement:

Statement I: This statement is correct. When a less volatile (high boiling point) solute is dissolved in a more volatile (low boiling point) solvent, the total vapour pressure of the solution \((P_s)\) can be higher than the vapour pressure of the pure solvent \((P_o)\). This happens because the solute disrupts the intermolecular forces between the solvent molecules, making it easier for them to escape into the vapor phase.

Statement II: This statement is false. Even with a more volatile solute, both the solvent and solute will contribute to the vapor pressure of the solution, although the contribution of the more volatile solute will be greater. The solution will have a combined vapor pressure that depends on the characteristics of both components.

Explanation:

Raoult's Law describes the relationship between the mole fraction of a non-volatile solute and the vapour pressure of the solution. However, for real solutions with volatile solutes, deviations from Raoult's Law occur. In the case of a less volatile solute in a more volatile solvent, the presence of the solute hinders the escape of solvent molecules, leading to a slight decrease in the expected increase in vapour pressure predicted by Raoult's Law. Nevertheless, the overall vapour pressure of the solution will still be higher than that of the pure solvent.

So, Statement I is true because adding a less volatile solute can increase the vapour pressure of the solution compared to the pure solvent. However, Statement II is false because both the solvent and solute contribute to the vapour pressure of the solution.