Why boiling point of water is increased on addition of sodium chloride into it ?

Explanation

When NaCl (or any other non-volatile solute) is dissolved in water, vapour pressure of water decreases (because some of the solvent molecules on the surface and replaced by the molecules of the solute which are non-volatile). The solution has to be heated more to make vapour pressure equal to the external pressure. Hence, boiling point is increased.