If the temperature of a liquid is increased, then its surface tension

Options

A. (a)Surface tension decreases while viscosity increases
B. (b)Surface tension increases while viscosity decreases
C. (c)Both increase
D. (d)Both decrease

Explanation

To solve the question regarding the effect of temperature on the surface tension of a liquid, we can follow these steps:

### Step-by-Step Solution:

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

2. **Effect of Temperature on Molecular Forces**:
- When the temperature of a liquid increases, the kinetic energy of the molecules also increases. This leads to a greater average distance between the molecules, which reduces the cohesive forces acting between them.

3. **Impact on Surface Tension**:
- Since surface tension is directly related to the cohesive forces among the liquid molecules, a decrease in these forces due to increased temperature will result in a decrease in surface tension.

4. **Understanding Viscosity**:
- Viscosity is a measure of a fluid's resistance to flow. It is influenced by the internal friction between the molecules of the liquid.

5. **Effect of Temperature on Viscosity**:
- As the temperature increases, the kinetic energy of the molecules increases, allowing them to move more freely. This results in a decrease in viscosity, as the liquid flows more easily.

6. **Conclusion**:
- From the above analysis, we can conclude that when the temperature of a liquid increases, the surface tension decreases and the viscosity also decreases.

### Final Answer:
The correct option is **D: Both surface tension and viscosity decrease**.

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