ANS:B - zero.

At the critical temperature, the surface tension of a liquid becomes indeterminate. This is because at the critical point, the distinction between the liquid and gas phases disappears, and the properties of the liquid undergo significant changes. As a result, the concept of surface tension, which is a property associated with the interface between a liquid and its vapor phase, becomes less meaningful at the critical point. Therefore, it is not possible to assign a definite value to the surface tension of the liquid at its critical temperature.