ICSE Class 8 Answered

It is the process whereby atoms or molecules in a liquid state gain sufficient energy to  escape from the surface of liquid and enter into the surrounding gaseous state environment.

It is the opposite process of condensation.

The thermal motion of a molecule of liquid must be sufficient to overcome the inter moleculer attractive forces (cohesive force) and evaporate,

that is, its kinetic energy must exceed  to overcome the cohesion at the surface.

Rate of evaporation therefore directly proportional to temperature.

Since only a small proportion of the molecules are located near the surface and are moving in the proper direction to escape at any given instant, the rate of evaporation is limited.

Also, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases.

This the reason that evaporating sweat cools the human body.