Question

In which among the following cases is adhesive force predominant over cohesive force?

• A. Water in capillary tube.
• B. Mercury in capillary tube.
• C. Water in a test tube in which the inner wall is coated with wax.
• D. Water on leaves of aquatic plants.

Answer 1

The correct option is A

Water in capillary tube.

Cohesive forces are forces that attract molecules of the same type. The attracting forces that occur between molecules of various types are known as adhesive forces.
Explanation for the correct option: (A)

1. The surface tension maintains the integrity of the surface.
2. Capillary action occurs when the adhesion to the walls is greater than the cohesive forces between the liquid molecules.

Explanation for the incorrect options: (B) Mercury has relatively low adhesive forces and strong cohesive forces with most container materials.

(C) The force of cohesion between water molecules is greater than the force of adhesion between water and wax molecules, water is depressed in a glass tube whose inner surface is coated with paraffin wax.

(D)

1. Capillary action is used by plants to transport water from the roots and stems to the rest of the plant
2. The attraction (cohesion) to the tree root tissue grows stronger than the attraction to other water molecules (adhesion).

Conclusion: Hence, the correct option is (A).