The spiders and insects move and run about on the surface of water without sinking because

$A$ molecule of water on the surface experiences:

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.

What are cohesive forces?

What is the maximum distance up to which the molecules can exert an attractive force on each other?

Define the surface of a liquid.