At critical temperature, the surface tension of a liquid

Options

A. is zero
B. is inifinity
C. is same as that it has at any other temperature
D. Cannot be determined

Answer

To solve the question regarding the behavior of surface tension at the critical temperature of a liquid, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Surface Tension**:
- Surface tension is defined as the force per unit length acting on the surface of a liquid. It arises due to the cohesive forces between liquid molecules.

2. **Effect of Temperature on Surface Tension**:
- As the temperature of a liquid increases, the kinetic energy of its molecules also increases. This increased energy causes the molecules to move more vigorously, which can weaken the cohesive forces between them.

3. **Critical Temperature Definition**:
- The critical temperature of a liquid is the highest temperature at which the liquid can exist in a distinct liquid phase. Above this temperature, the liquid and vapor phases become indistinguishable.

4. **Behavior at Critical Temperature**:
- At the critical temperature, the thermal energy is so high that the cohesive forces between the molecules are completely overcome. As a result, the surface tension, which relies on these cohesive forces, becomes zero.

5. **Conclusion**:
- Therefore, at the 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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