Assertion: Oil drops spread on cold water and remain as a drop on hot water.
Reason : Surfnce tension of oil is less than cold water and more than that of hot water.

Options

A. If both assertion and reason are correct and remad is a correct explanation of the assertion.
B. If both assertion and reason are correct bat reason is not the correct explanation of assertion.
C. If assertion is correct but reason is incorrect.
D. If assertion is incorrect but reason is correct.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that oil drops spread on cold water but remain as a drop on hot water.
- This implies that the behavior of oil in relation to water changes with temperature.

2. **Understanding Surface Tension**:
- Surface tension is a property of liquids that causes them to behave as if their surface is covered with a stretched elastic membrane.
- It is influenced by the cohesive forces between liquid molecules.

3. **Analyzing Cold Water**:
- When oil is placed on cold water, it spreads out.
- This indicates that the surface tension of oil is less than that of cold water.
- Since the oil has a lower surface tension, it can overcome the surface tension of cold water and spread out.

4. **Analyzing Hot Water**:
- Conversely, when oil is placed on hot water, it remains as a drop.
- This suggests that the surface tension of oil is greater than that of hot water.
- A higher surface tension means that the oil molecules are more attracted to each other than to the water, causing the oil to maintain a spherical shape instead of spreading.

5. **Conclusion**:
- The reason provided states that the surface tension of oil is less than that of cold water and more than that of hot water, which explains the behavior of oil in both scenarios.
- Therefore, both the assertion and the reason are correct, and the reason correctly explains the assertion.

### Final Answer:
- The correct option is **Option 1**: Both assertion and reason are correct, and the reason is a correct explanation for the assertion.