Statement I: Addition of a non-volatile solute to a volatile solvent increases the boiling point.

Statement II:  Addition of non-volatile solute results in lowering of vapour pressure.

If both statements are CORRECT, and Statement II is the CORRECT explanation of Statement I.

The correct answer is option 1. If both statements are CORRECT, and Statement II is the CORRECT explanation of Statement I.

Statement I: Addition of a non-volatile solute to a volatile solvent increases the boiling point.

This phenomenon is known as boiling point elevation. When you add a non-volatile solute (like salt or sugar) to a volatile solvent (like water), the solute particles interfere with the solvent molecules’ ability to escape into the vapor phase. This means that the solvent needs to be heated to a higher temperature to reach the vapor pressure necessary for boiling.

Statement II: Addition of a non-volatile solute results in lowering of vapor pressure.

This is known as vapor pressure lowering. When a non-volatile solute is added to a solvent, it occupies space at the surface of the liquid and reduces the number of solvent molecules that can escape into the vapor phase. As a result, the vapor pressure of the solvent decreases because there are fewer solvent molecules in the vapor phase.

Relationship Between the Statements

The lowering of vapor pressure (Statement II) is the reason behind the boiling point elevation (Statement I). Because the vapor pressure is reduced, the solvent needs to be heated to a higher temperature to reach the point where its vapor pressure equals the external pressure, thus boiling at a higher temperature.

Conclusion: Since the addition of a non-volatile solute lowers the vapor pressure, which in turn causes the boiling point of the solution to increase, Statement II explains why Statement I is true. Therefore, Option 1 is correct: both statements are correct, and Statement II correctly explains Statement I.