Question

why does the capillary rise increase when the diameter of the tube decreases?

Answer 1

Since water is polar, the cohesion of water causes capillary attraction, the ability ofwater to move uphill in small spaces.

A thinner tube has less surface area and so the water molecules have less space to fill and that's why they rise higher in a thin tube then a thick tube.

This is the reason why the capilliary rise increase when the diameter of the tube decreases.