Why does a solution containing non-volatile solute have higher boiling point than a pure solvent? Why is elevation of boiling point a colligative property?

Boiling point is the temperature at which vapour pressure of a solution becomes equal to atmospheric pressure.When a solute is added in a solution, the vapour pressure decreases.This is due to the number of pure solute particles on the surface decreasesthereby the number of solute particles escaping from the surface also decreases. Therefore, as the vapour pressure decreases, more temperature is required to bring the vapour pressure of solution to atmospheric pressure and hence,boiling point increases.

A colligative property depends on the number of solute particles, it does not depend on the identity of particles. As the number of solute particles increases, the boiling point also increases.