Temperature of water at the surface of lake is `- 20^(@)C`. Then temperature of water just below the lower surface of ice layer is

Options

A. `- 4^(@)C`
B. `0^(@)C`
C. `4^(@)C`
D. `-20^(@)C`

Explanation

To solve the problem, we need to understand the relationship between the temperature of water at the surface of the lake and the temperature of the water just below the ice layer.

### Step-by-Step Solution:

1. **Identify the Temperature at the Surface**:
The temperature of the water at the surface of the lake is given as -20°C.

2. **Understand the Ice-Water Interface**:
At the interface between ice and water, we need to consider the equilibrium between the two phases. Ice is at 0°C when it is in equilibrium with water at the same temperature.

3. **Temperature of Water Below Ice**:
The water just below the lower surface of the ice layer must be at the same temperature as the ice, which is 0°C. This is because at the ice-water interface, the temperature remains constant during the phase change (melting of ice).

4. **Conclusion**:
Therefore, the temperature of the water just below the lower surface of the ice layer is 0°C.

### Final Answer:
The temperature of water just below the lower surface of the ice layer is **0°C**.

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