At critical temperature, the surface tension of a liquid

Options

A. is zero
B. is infinity
C. is same as that at any other temperature
D. cannot be determined

Answer

To solve the question regarding the surface tension of a liquid at its critical temperature, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Critical Temperature**:
- The critical temperature of a substance is defined as the temperature above which a gas cannot be liquefied, regardless of the pressure applied. At this temperature, the distinction between the liquid and gas phases disappears.

2. **Behavior of Molecules at Critical Temperature**:
- At the critical temperature, the cohesive forces between the molecules of the liquid become very weak. This is because the kinetic energy of the molecules is high enough to overcome the intermolecular forces that typically hold the liquid together.

3. **Surface Tension Concept**:
- Surface tension is the result of cohesive forces between liquid molecules at the surface. It is what allows liquids to resist an external force and is responsible for the shape of liquid droplets.

4. **Surface Tension at Critical Temperature**:
- Since the cohesive forces are significantly reduced at the critical temperature, the surface tension, which relies on these forces, also approaches zero. This means that at the critical temperature, the liquid behaves more like a gas, and the surface tension is effectively eliminated.

5. **Conclusion**:
- Therefore, at critical temperature, the surface tension of a liquid is zero.

### Final Answer:
At critical temperature, the surface tension of a liquid is zero.

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