what is the phenomenon of capillarity ? derive an expression for the rise of liquid in a capillary tube .

The phenomenon of rise or fall of liquid in a capillary tube is called capillarity action.
Follow the link given below to get the derivation of rise of a liquid in a capillary tube (Ascent formula) :-
https://www.meritnation.com/ask-answer/question/an-expression-for-the-rise-of-liquid-in-a-capillary-tu/mechanical-properties-of-fluids/3706364