Read the Passage and answer the following question:

There are many properties of ideal solutions which depends only on the concentration of the solute particles and are independent of the nature of the solute. Such properties are called colligative properties. For example, when a non-volatile solute is added to a solvent, its vapour pressure gets lowered. Raoult established that relative lowering in vapour pressure depends only on the concentration of the solute and it is independent of its identity. Similarly, elevation in boiling point, depression in freezing point and osmotic pressure on addition of a non volatile solute to a solvent depend only on the concentration of solute but are independent of its nature. These properties can also be used to determine the molar mass of the solute. The relative lowering in vapour pressure changes when the solute is electrolyte and undergoes association or dissociation in the solution. The molar mass obtained in these electrolytic solutions are abnormal molar masses.

Which of the following is a colligative property?

Relative lowering in vapour pressure

The correct answer is option 2. Relative lowering in vapour pressure.

The colligative properties are those properties of solutions that depend solely on the number of solute particles present in the solution, not on the identity of the solute particles. These properties are affected by the concentration of solute particles in the solution, not the nature of the solute itself.

Among the options provided, the colligative property is relative lowering in vapor pressure.

1. Lowering in Vapor Pressure:

When a non-volatile solute is added to a solvent, the vapor pressure of the resulting solution decreases compared to that of the pure solvent. This lowering in vapor pressure is a colligative property because it depends on the concentration of solute particles in the solution, not the identity of the solute particles. The magnitude of the lowering in vapor pressure is directly proportional to the concentration of the solute particles and is described by Raoult's law.

2. Relative Lowering in Vapor Pressure:

Relative lowering in vapor pressure is a specific expression of the colligative property of vapor pressure lowering. It is defined as the ratio of the lowering in vapor pressure of the solution to the vapor pressure of the pure solvent. It is used to characterize the extent of the vapor pressure reduction in a solution compared to the pure solvent and is also a colligative property.

3. Vapor Pressure of Solution:

The vapor pressure of the solution itself is not a colligative property because it depends on both the nature and concentration of the solute particles. While the vapor pressure of the solution is influenced by the presence of solute particles, it is not considered a colligative property because it is not solely dependent on the number of solute particles.

4. Boiling Point of Solution:

The boiling point of a solution is not a colligative property because it depends on both the identity and concentration of the solute particles. While adding a non-volatile solute to a solvent raises the boiling point of the solution, the effect is not solely dependent on the number of solute particles and is therefore not a colligative property.

Among the options provided, the colligative property is the lowering in vapor pressure, as well as its specific expression, the relative lowering in vapor pressure.