Question

Radius of an air bubble in deep water increase or decrease with depth

Answer 1

Surface tension is a collection of cohesive forces between the molecules of a liquid, at the surface of the liquid, thereby binding them together. But these aren't so strong and could handle forces up to an extent of 0.1N approx.
This is an important property of fluids which can explain the phenomenon of capillarity in tubes, shape of a drop, concavity or convexity of liquid surfaces in different tubes of different materials