Question

No heat is supplied to a liquid during evaporation. How does then the liquid change into its vapour?

Answer 1

Even though no heat is supplied the liquid changes to vapour.it occurs by the process of evaporation.
Evaporation is a process in which the surface molecules get escaped from the liquid to mix up with air and hence the water level decreases.

During evaporation, particles of water absorb heat from the surroundings to change their state. The particles at the surface absorb more heat and change into vapour.

The evaporated liquid molecules get mixed with atmosphere and forms humidity in air.