Explain why water does not run out of a dropper unless its rubber bulb is pressed.

$A$ molecule of water on the surface experiences:

When drops of mercury are placed on a clean surface of glass,they merge and become a single drop. Explain.

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

Mercury does not wet glass,wood,or iron 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.