Surface tension is due to

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

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.

$A$ drop of oil is placed on the surface of water. Which of the following statements is correct?

Force in Column-$I$ and its use in Column-$II$ are given. Match them appropriately.

Column-$I$	Column-$II$
$(a)$ Cohesive force	$(i)$ Useful for writing by chalk on blackboard.
$(b)$ Adhesive force	$(ii)$ Useful in soldering.
	$(iii)$ Useful for formation of spherical drops of liquid.

Mercury does not wet glass,wood,or iron because