Question

At a critical point, the meniscus between liquid and vapor disappears due to
A. Zero refractive index
B. Zero surface tension
C. Zero viscosity
D. Zero vapor pressure

Answer 1

The critical point is that the temperature and pressure at which the differentiation between liquid and gas can now not be made. The physical phenomenon of surface tension is the tendency of liquid surfaces to shrink to the minimum extent possible.

Complete step by step answer:
To understand this we need to understand what's the effect of temperature and pressure on
liquids and gases, respectively.
On increasing the temperature, the density of a liquid decreases and whereas if the pressure applied on the gas is increased, the density will also increase.
● As soon as it approaches its critical point, both the states approach towards the identical density and exist in a very single-phase, referred to as Supercritical Fluid. During this phase, it exhibits most of the properties of the gas.
When the critical temperature point is attained, the liquid and gas phase will disappear.
● At the crossroads, the particles in an exceedingly closed container are thought to be vaporizing at such a rapid rate that the density of liquid and vapor are equal and thus form a supercritical fluid. As a result of the high rates of change, the surface tension of the liquid eventually disappears. Therefore, the answer is zero surface tension.
The correct answer is option B.

Note:
The condensation of gas will never occur above the critical point. A large amount of pressure may be applied to a gas in a very closed container, and it's going to become highly dense, but won'to exhibit a meniscus. Molecules at critical temperatures possess high kinetic energy, and as a result, the intermolecular forces within the molecules are weakened.