Ice is formed on the top surface of a lake. Temperature of air above ice is `-15^(@)C`, (i) What is the temperature of the water layer just below ice? (ii) Find the maximum possible temperature at the bottom of the lake.

Explanation

(i) The temperature of the water layer just below the frozen surface is `0^(@)C`. A thick ice layer acts as a good insulator that prevents heat from escaping to the outer atmosphere. So the water below does not freeze easily.
(ii) Maximum temperature can be `4^(@)C` at the bottom of the lake. As the density of water is maximum at `4^(@)C`, water of this temperature occupies the bottom.