A block of wood is floating in water at `0^@ C`. The temperature of water is slowly raised from `0^@ C` to `10^@ C`. How will the precentage of volume of block above water level change with rise in temperature?

Explanation

To solve the problem, we need to analyze how the density of water changes with temperature and how this affects the floating block of wood.

### Step-by-Step Solution:

1. **Understanding the Initial Condition**:
- At `0°C`, the block of wood is floating in water. The percentage of the volume of the block above the water level is determined by the balance of forces acting on it, specifically the buoyant force and the weight of the block.

2. **Density of Water at Different Temperatures**:
- The density of water is maximum at `4°C`. As the temperature of water increases from `0°C` to `4°C`, the density of water increases. After `4°C`, the density of water decreases as the temperature continues to rise to `10°C`.

3. **Effect of Temperature on Buoyancy**:
- When the temperature of the water is raised from `0°C` to `4°C`, the density of water increases. Since the density of the water is increasing, the buoyant force acting on the block of wood also increases. This means that the block will float higher, and the percentage of the volume of the block above the water level will increase.

4. **Transition at `4°C`**:
- At `4°C`, the density of water is at its maximum. The block of wood will be floating at a certain level where the weight of the block equals the buoyant force.

5. **Raising Temperature from `4°C` to `10°C`**:
- As the temperature continues to rise from `4°C` to `10°C`, the density of water decreases. Consequently, the buoyant force acting on the block of wood decreases. Since the density of the wood remains constant, the block will start to sink slightly deeper into the water, leading to a decrease in the percentage of the volume of the block above the water level.

6. **Conclusion**:
- Therefore, the percentage of the volume of the block above the water level first increases as the temperature rises from `0°C` to `4°C`, and then decreases as the temperature rises from `4°C` to `10°C`.

### Final Answer:
The percentage of volume of the block above the water level first increases from `0°C` to `4°C` and then decreases from `4°C` to `10°C`.