explain surface tension and capillary action

Surface tension is a property of liquids that occurs due to the cohesive forces between molecules at the surface. At the surface, molecules do not have other like molecules on all sides of them, and consequently, they cohere more strongly with those directly associated with them on the surface. This creates a sort of 'film' that makes the surface layer of a liquid more resistant to an external force.

A familiar example of surface tension is the ability of water to form droplets on a smooth surface or the ability of some insects to walk on water. The surface acts like an elastic film. Surface tension is responsible for the shape of liquid droplets and bubbles, and for the capillary waves on the surface of liquids.

Capillary action, also known as capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. It occurs because of the intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to lift the liquid.