The colligative properties of a solution are those which depend on the number of particles (and hence the amount) of solute dissolved in a given quantity of solvent, irrespective of the chemical nature of those particles. We have already seen from Raoult’s law that the vapor pressure of a solution depends on the mole fraction of solute (amount of solute), and now we are in a position to see how this affects several other properties of solutions.
In the image below, there are two solutions. Both have a dark blue solvent and the same number of solute particles dissolved in said solvent, light blue particles on the left and green particles on the right. A colligative property is a property that would be the same for both of the solutions below, even though they contain different solutes. Since they contain the same number of solute particles, any colligative properties of the solutions would be identical.