A drop of water is sprinkled on a red hot iron plate.The drop forms a small sphere but does not vaporise immediately. This happens because :

Options

A. Red hot iron is a poor conductor of heat
B. A layer ofwater vapour between the drop and plate prevents conduction of heat
C. Boiling point of water is raised
D. Of some other reason

Explanation

To solve the question regarding why a drop of water sprinkled on a red-hot iron plate forms a small sphere but does not vaporize immediately, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Scenario**:
- A drop of water is placed on a red-hot iron plate. The plate is at a high temperature, which typically would cause the water to vaporize quickly.

2. **Observation of the Drop**:
- Instead of vaporizing, the water drop forms a small sphere on the surface of the iron plate. This indicates that the water is not in direct contact with the hot surface.

3. **Formation of Water Vapor Layer**:
- As the water drop comes into contact with the hot iron, it begins to heat up. However, before it can vaporize completely, a layer of water vapor forms between the drop and the iron plate.

4. **Effect of the Water Vapor Layer**:
- This layer of water vapor acts as an insulating barrier. It prevents efficient conduction of heat from the hot iron plate to the water drop.

5. **Conclusion**:
- The reason the water drop does not vaporize immediately is due to the formation of this insulating layer of water vapor, which inhibits heat transfer. Therefore, the correct explanation is that the layer of water vapor between the drop and the plate prevents conduction of heat.

### Final Answer:
The drop of water does not vaporize immediately because a layer of water vapor forms between the drop and the red-hot iron plate, preventing efficient heat conduction.