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Capillary action of the liquid can be explained on the basis of its ___
A. Resistance to flow
B. Surface tension
C. Heat of evaporation
D. Refractive index

Answer
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Hint: Think about what exactly is the interaction between the liquid in question and the walls of the capillary, how it may affect the level of water in the tube, and the forces involved.

Complete answer:
Capillary action is the ability of a fluid to flow through a narrow tube without the aid of any outside force or even in the opposition of gravity.
We know that the capillaries are the small narrow cylindrical tubes having very small diameter. A capillary dipped inside a fluid will show either a rise or fall relative to its surrounding fluid based on the type of fluid present.
The reason for this capillary rise is adhesive and cohesive forces. Adhesive forces are the intermolecular forces between molecules of two different substances and cohesive forces are the intermolecular forces between the molecules of the same substance.
If the adhesive force of a liquid with the material of the capillary is greater than the cohesive forces of the liquid, then a rise in the level of liquid inside the capillary can be seen. For example, water and glass. On the other hand, if the cohesive forces are greater than the adhesive forces, a fall in the level can be seen. For example, mercury and glass.
These interactions between the adhesive and cohesive forces together are responsible for the surface tension of any given liquid. This in turn causes the capillary action.
So, the capillary rise of a liquid can be explained on the basis of its surface tension. Therefore, the correct option is ‘B’.

Note: We know that the surface tension of liquid results from an imbalance of intermolecular attractive forces which is the cohesive forces between the molecules. The tendency of liquid to shrink into the minimum surface area possible is the surface tension.
To remember the difference between adhesive and cohesive forces, recall the name ‘adhesive glue’ which is used to stick two different materials together, link this to the intermolecular forces between two different materials.