In what direction does the force act on a molecule at the surface of a liquid? Explain.

$A$ liquid is at rest in a container. In a sphere of influence, the liquid molecule at its centre is

Show that the force exerted by a fluid at rest is perpendicular to its contact surface.

Water does not wet an oily glass because

Explain why:
$(a)$ The angle of contact of mercury with glass is obtuse,while that of water with glass is acute.
$(b)$ Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently,water wets glass while mercury does not.)
$(c)$ Surface tension of a liquid is independent of the area of the surface.
$(d)$ Water with detergent dissolved in it should have small angles of contact.
$(e)$ $A$ drop of liquid under no external forces is always spherical in shape.

Explain surface tension in the context of potential energy.