What are colligative properties?

Colligative properties are those that depend specifically on the number of solute particles present in a solution, rather than on the identity or chemical nature of the solute itself. This means that it is the quantity of particles—be they molecules or ions—that affects the properties of the solution, leading to changes such as boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

For instance, when a non-volatile solute is added to a solvent, the vapor pressure above the solution decreases because the presence of solute particles interferes with the escape of solvent molecules into the vapor phase. The extent of this vapor pressure lowering depends solely on how many solute particles are added, not on what the solute is. This principle applies universally to any type of solute, making colligative properties a fundamental concept in understanding the behavior of solutions.

While the concentration of the solute does influence these properties, it is the total number of solute particles that plays the critical role, rather than the specific nature of the solute. This distinction is what makes the correct answer particularly relevant in discussions of colligative properties.