The water on the surface of a lake is just about to freeze. What will be the temperature of water at the bottom of the lake?

When the water on the surface of a lake is just about to freeze, the temperature of the water at the bottom of the lake will be approximately 4°C. This is due to the unique property of water where it reaches its maximum density at 4°C. As the surface water cools down to 0°C and begins to freeze, it becomes less dense and remains on top, while the denser water at 4°C sinks to the bottom. This process ensures that the bottom of the lake remains at a relatively constant temperature of 4°C, providing a stable environment for aquatic life during winter. The layering effect, known as thermal stratification, prevents the entire lake from freezing solid, thus preserving the ecosystem within. Therefore, the correct answer is [D] 4° C.