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

Explanation

(i) This because of the unique property of water as a result of which it has maximum density and minimum volume at `4^(@)C`. Thus while the surface of the take freezes in severse cold, the water beneath the surface is still at `4^(@)C` as it is heavier than the water on the surface. Hence, the top of the lake freezzes first and the water inside can freeze in case the temperature is sub-zero
(ii) For answer, consult section 9.7