At the critical point of a substance
A
The surface tension vanishes
B
Liquid and vapour have the same density
C
There is no distinction between liquid and vapour phases
D
All of the above
Correct Answer: All of the above
A critical point is a point where the physical distinction between the liquid and vapor vanishes since there will be no further difference in properties like surface tension, volume, density etc. Between the liquid and vapor. So we call the state of substance at and above the critical point as gas.