Question

give reason why earthen pots are wrapped with a wet cloth during summer

Answer 1

The summer heat being at its maximum, evaporates the water from the 
wet cloth and makes it dry.The earthen pot being porous,the outside 
heat draws out the water from it which is taken up by the dry cloth ultimately making it wet. As this cycle of wetting and drying of the cloth continues, the water in the pot remains cool. 
In India, such earthen pots are kept by the roadside by the religious and kind people for the thirsty people to quench their thirst in very hot weather.

Answer 2

In summer,the water inside the earthen potholes evaporating through the small pores of the pot by taking heat from the earthernpot, then makes the pot and the water inside the pot be cool. So to avoid the vapourisation and the loss of water,the earthen pot is wrapped with wet clothes.