Given reasons
(i) Lakes freeze form top towards bottom.
(ii) Ice floats on water.

Explanation

(i) During severe winter, the temperature of water in the lake keeps on decreasing . Since cold water is heavier, therefore, it keeps on going into the interior of the lake while warm water from inside the lake keeps on coming to the surface of the lake. This process continues till the temperature of entire water of the lakes becomes 277 K. Since denisty of water is maximum at 277 K , therefore, any further decrease in the temperature of the surface water will decrease its density . As a result , the temperature of the surface water keeps on decreasing and ultimately freezes while the temperature of water underneath the surface remains at 277 K . Further decrease in the temperature of ice on the surface will decrease the temperature of water below 277 K lying underneath the surface of water. This decrease in temperature continues till it freezes. This process continues and as a result , the lakes keeps on freezing from top to bottom.