On heating a liquid its surface tension

Options

A. Increases
B. Decreases
C. Remains same
D. Is reduced to zero

Answer

**Step-by-Step Solution:**

1. **Understanding Surface Tension**:
- Surface tension is defined as the cohesive force of attraction between similar molecules at the surface of a liquid. This force causes the liquid to behave as if its surface is covered with a stretched elastic membrane.

2. **Effect of Heating on Molecules**:
- When a liquid is heated, the temperature increases, which leads to an increase in the kinetic energy of the molecules. This means that the molecules move more vigorously.

3. **Impact on Cohesive Forces**:
- As the kinetic energy of the molecules increases, the cohesive forces (the forces of attraction between similar molecules) become less effective. This is because the increased movement allows molecules to overcome these attractive forces more easily.

4. **Consequences for Surface Tension**:
- Since surface tension is directly related to the cohesive forces among the molecules, a decrease in these forces due to increased molecular movement results in a decrease in surface tension.

5. **Conclusion**:
- Therefore, when a liquid is heated, its surface tension decreases. The correct answer to the question is option B: "may decrease."