Question

At critical temperature, the surface tension of a liquid is given by
A. zero
B. infinity
C. the same at any other temperature
D. none of these

Answer 1

Hint: The critical temperature of a substance is defined as the temperature at and above which the vapour state of a substance cannot be converted into its liquid state, no matter how much pressure is applied. Each and every substance is having a specific critical temperature.

Complete step by step answer:
First of all let us take a look at what actually the surface tension and critical temperature actually means. Surface tension is the phenomena in which liquid surfaces are having a tendency to shrink into the minimum surface area possible. Surface tension permits objects usually denser than water, to float and slide on a water surface. A molecule in the huge amount of liquid experiences cohesive forces which is with other molecules in all the possible directions. A molecule at the surface of a liquid feels only resultant inward cohesive forces. The critical temperature of a gas is the amount of the strength of the intermolecular attractive forces. In general it is seen that, as the temperature increases, the surface tension is getting reduced so that at possible higher temperature, it will be minimum. Therefore at the critical temperature, the surface tension will be zero.
Hence the correct answer for this question is option A.

Note:
The critical temperature is dependable on the strength of the intermolecular interactions. As the intermolecular forces are weaker, then it is more difficult to liquefy that gas or convert the state and hence lower would be the critical temperature of that gas.