During summer days, water kept in an earthen vessel cool. This happens due to the following phenomenon

During summer days, water kept in an earthen vessel stays cool primarily due to the phenomenon of evaporation. The porous structure of the earthen material allows water to slowly seep through its surface. Once on the outer surface, water molecules evaporate into the air, taking away latent heat from the remaining water inside the vessel. This process continues, leading to a continuous removal of heat from the water, thereby keeping it cool. Unlike other options such as diffusion, transpiration, or osmosis, which involve the movement of substances through membranes or diffusion gradients, evaporation specifically refers to the conversion of liquid water into vapor, usually at the surface of a liquid. Understanding this cooling effect of evaporation is crucial in various contexts, such as traditional cooling methods, climate control strategies, and the design of evaporative cooling systems for buildings or refrigeration units. Therefore, the correct answer is [D] Evaporation.