Capilary action of the liquid can be explained on the basis of its

Options

A. resistance to flow
B. surface tension
C. heat of vaporisation
D. refractive index

Answer

### Step-by-Step Solution:

1. **Understanding Capillary Action**:
- Capillary action refers to the ability of a liquid to flow in narrow spaces without the assistance of external forces. This phenomenon is commonly observed when a thin tube (capillary) is placed upright in a liquid.

**Hint**: Think of how water rises in a straw or a thin tube.

2. **Identifying the Forces Involved**:
- Capillary action is influenced by two main types of intermolecular forces:
- **Adhesive Forces**: These are the attractive forces between the molecules of the liquid and the molecules of the material of the capillary.
- **Cohesive Forces**: These are the attractive forces between the molecules of the same liquid.

**Hint**: Remember that adhesive forces pull the liquid towards the capillary walls, while cohesive forces hold the liquid molecules together.

3. **Analyzing the Conditions for Rise or Fall**:
- If the adhesive forces are greater than the cohesive forces, the liquid will rise in the capillary tube (this is known as capillary rise).
- Conversely, if the cohesive forces are greater than the adhesive forces, the liquid will not rise and may even fall in the capillary tube (this is known as capillary depression).

**Hint**: Visualize how water behaves in a thin glass tube versus how it behaves in a wider container.

4. **Relating to Surface Tension**:
- Both adhesive and cohesive forces are closely related to the concept of surface tension. Surface tension is the property of the liquid's surface that allows it to resist an external force due to the cohesive nature of its molecules.
- Therefore, surface tension plays a crucial role in determining the extent of capillary action.

**Hint**: Think of surface tension as the "skin" on the surface of the liquid that helps it climb up the walls of the capillary.

5. **Conclusion**:
- Given the options provided (resistance to flow, surface tension, heat of vaporization, refractive index), the correct explanation for capillary action is **surface tension**.

**Final Answer**: The capillary action of the liquid can be explained on the basis of its **surface tension**.