The loss of water in the form of water vapour through stomata on leaves is known as

a) Distillation is the process by which a mixture of liquids is separated into its components.

b) Diffusion is the passive movement of molecules along their concentration gradient.

c) Osmosis is the movement of water molecules from less concentrated solution to a more concentrated solution through a semipermeable membrane.

d) Transpiration is the evaporation of water from the leaves through minute pores called stomata.

So, the correct answer is D.