Question

water stored in an earthen vessel become cool

Answer 1

because earthern vessels contain small pores which continue touch with moisture. the water in the earthern vessels continuously evaporated and kept water cool in it

Answer 2

water stored in an earthen vessel became cool this can be explained as follow : the earthen vessel has large number of small pores in its wall some of the water continusely keep on seeping from these pores to the outside of vessel this water tskes the latent heat required for vapourisation fron the remaining water in the vessel and get evaporate quickly hence the remaining water loose heat and became cool
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