Most substances contract on freezing . However, water does not belong to this category. We know that water expands on freezing. Further , coefficient of volume expansion of water in the temperature range from `0^(@)C` to `4^(@)C` is negative and above `4^(@)C` it is positive . This behaviour of water shapes the freezing of lakes as the atmospheric temperature goes down and it is still above `4^(@)C`.
As the atmospheric temperature goes below `4^(@)C`

Options

A. Cooled water at the surface flows downward because of its greater density
B. Cooled water at the surface does not flow downward and remains at the surface because its smaller density
C. Cooled water at the surface downward because of its density
D. Temperature of water in the lake reduces with depth

Answer

B

Explanation

At temperature below `4^(@)C` , temperature above is less as compared to below & thus water remain is it is due to higher volume at the upper surface.