ANS:C - both (a) & (b)

The rise of liquid in a capillary tube is primarily due to adhesion.

Explanation:

1. Adhesion:
   • Adhesion is the attraction between molecules of different substances. In the context of a capillary tube, adhesion refers to the attraction between the molecules of the liquid and the molecules of the solid (the material of the capillary tube).
   • When the adhesive forces between the liquid molecules and the solid surface of the capillary tube are stronger than the cohesive forces between the liquid molecules themselves, the liquid climbs or rises in the capillary tube.
2. Cohesion:
   • Cohesion is the attraction between molecules of the same substance. While cohesion is important in maintaining the continuity and surface tension of the liquid column, it is not the primary reason for the rise of liquid in a capillary tube.
3. Capillary Action:
   • Capillary action occurs because of the combined effect of adhesive and cohesive forces. The liquid rises in a capillary tube due to the balance between these forces, with adhesion playing a crucial role in pulling the liquid up against the force of gravity.
4. Options Analysis:
   • Both (a) & (b): This option suggests that both cohesion and adhesion contribute to capillary rise, which is true to some extent, but adhesion is the primary reason for the rise of liquid in a capillary tube.
   • Neither (a) nor (b): This option is incorrect because adhesion does indeed play a significant role in capillary rise.

Conclusion: