Question

The surface tension of a liquid at its boiling point is:
(A) maximum
(B) zero
(C) same as at room temperature
(D) minimum but more than zero

Answer 1

Hint
Boiling point, temperature at which the pressure exerted by the surroundings upon a liquid is equaled by the pressure exerted by the vapour of the liquid; under this condition, addition of heat results in the transformation of the liquid into its vapour without raising the temperature.

Complete step by step answer
Let us assume the liquid is water, factors affecting the surface tension:-
The presence of impurities either on the surface or dissolved in it , affect surface tension of liquid. Highly soluble substances increase the surface tension of water whereas sparingly soluble substances decrease the surface tension.
The surface tension of liquid decreases with increase in temperature. The surface tension of a liquid becomes zero at its boiling point and vanishes at critical temperature. As the temperature increases, surface tension decreases. At the boiling point, every molecule of a liquid is in motion from bottom to surface, and due to rise in temperature, molecules lose the adhesion and hence, surface tension becomes zero.
Option (B) is correct.

Note
Surface tension is an effect where the surface of a liquid is strong. The surface can hold up a weight, and the surface of a water droplet holds the droplet together, in a ball shape. Some small things can float on a surface because of surface tension, even though they normally could not float.