95. The surface of a lake is frozen in severe winter, but the water at its bottom is still liquid. What is the reason ?

(a) Ice is a bad conductor of heat.

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(b) Since the surface of the lake is at the same

temperature as the air, no heat is lost.

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(d) None of the statements (a), (b) and (c) given is correct.

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Solution

The correct option is A
(a) Ice is a bad conductor of heat.

(A)
When temperature starts reducing in winter, lake
water cools upto 4 degree centigrade by convection

as density increase with reduction in temp. On further

cooling, due to abnormal expansion of water, density

reduces and cold water remains at top. Then top layer

freezes. Ice being bad conductor of heat, lake water

below ice remains at 4 degrees.

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