Which of the following is not a colligative property?

Lowering in vapour pressure

The colligative properties are properties of a solution that depend only on the number of solute particles and not on the nature of the solute particles. These properties are proportional to the concentration of the solute and play a significant role in determining the behavior of solutions.

The property that is not a colligative property is:

(3) Lowering in vapor pressure

Lowering in vapor pressure is not a colligative property because it does depend on the nature of the solute particles. The vapor pressure of a solution is influenced by the presence of solute particles, but it also depends on the nature of the solute-solvent interactions, which is not solely determined by the number of solute particles. In contrast, the other three properties mentioned: elevation in boiling point, depression in freezing point, and osmotic pressure, are colligative properties as they depend solely on the concentration of solute particles and not on the specific identity of the solute particles.