Question

Explain why surface tension of a liquid is independent of the area of the surface.

Answer 1

we know, the force acting per unit length at the interface between the plane of a liquid and any other surface is known as surface tension.
from definition, surface tension = force/length

it is also clear that force doesn't depend on area of the surface. because force is just product of mass and acceleration. so, surface tension of a liquid is independent of the area of surface.

Answer 2

The liquid molecules which are below the surface are in equilibrium.  The liquid molecules which are at the surface are attracted by other molecules in downward direction. So, a force is originated to balance the surface molecules which is equal but opposite in direction to the downward force. This force is called surface tension.