Question

Surface tension does not vary with:
A.temperature
B.vapour pressure
C.the size of the surface
D.concentration

Answer 1

Surface tension is mainly the property of liquids. It can be calculated as the force per unit length of the molecules at the surface. This property allows the molecules to shrink using forces of attraction to occupy a minimum surface area.

Complete answer:
Let us consider the variance of surface tension one by one with given parameters.
Surface tension varies with temperature. It is because as the temperature increases the molecules on the surface move apart from each other. This result in the force of attraction between molecules goes weaker and hence surface tension decreases as temperature increases.
Vapour pressure is the property of liquid where the molecules have to overcome the surface forces and go into the vapour phase. So the increase or decrease of vapor pressure will directly affect the surface tension. Here also the molecules can remain close or go apart by decrease or increase of vapor pressure. Hence surface tension varies with vapor pressure.
The size of the surface will not vary the surface tension. The reason is the molecules having forces of attraction per unit length do not change with the size of the surface. In other words, the size of the surface is independent of the force or the length of the molecule present at the surface.
Concentration will definitely vary the surface tension. With an increase or decrease in the concentration of liquid, the number of molecules which remain close or apart changes. As a result, the forces of attraction change and affects surface tension.
Hence option C is the correct answer. Surface tension is not affected by the size of the surface.

Note:
Surface tension is a surface phenomenon and should not be confused with the bulk of the substance. The word tension means some kind of forces that are present at the surface making some impact. The forces of attraction between molecules at the surface indicate whether they are close or apart.