Question

If the surface of the water in a lake is just going to freeze, then the temperature of water at the bottom is
A) $0^\circ{\text{C}}$
B) $4^\circ{\text{C}}$
C) $3^\circ{\text{C}}$
D) None of these

Answer 1

The water shows some anomalous behavior at a particular temperature. This property of water has to be studied. The surface of water found to be floated hence less dense.

Complete step by step answer:
In most of the liquids when the temperature increases the volume increases and thus the density will be less. In reverse when the temperature decreases, the volume will be decreased. This is the normal behavior of water. Water shows this property for all the temperatures above ${4^\circ }{\text{C}}$.
But the water shows anomalous behavior in the temperature range ${0^\circ }{\text{C}}$ to ${4^\circ }{\text{C}}$. Thus in this range of temperature when the temperature increases the volume will decrease. Thus the water will be less dense.
We have the temperature of the surface water of the lake is above ${4^\circ }{\text{C}}$. When we freeze the surface, the temperature is lowered to ${4^\circ }{\text{C}}$. At that time of temperature decrease, the volume decreases and the density is more. The denser water will sink down the bottom and the bottom water having less dense will comes up to the surface. Again the surface water reaches below ${4^\circ }{\text{C}}$, the volume will increase making the water less dense. Thus it will float at the top and freezes. The freezer layer at the top will insulate the bottom layer of water. Thus the temperature of the bottom will be maintained at ${4^\circ }{\text{C}}$.

Therefore, the answer is option B.

Note:
The anomalous behavior of the water helps the aquatic animals to live in low temperatures. The water will maintain a certain temperature below the ice on the surface of water resources. This helps for oxygen availability for the aquatic creatures.