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Question

State reason for unsolidification of water inside lakes in cold countries?

A
anomalous expansion of water
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B
thermal conductivity of water
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C
High specific heat capacity of water
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D
Data insufficient
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Solution

The correct option is A anomalous expansion of water
Answer: A
Firstly, let me give you a little basic knowledge about a property of liquids, then i'll proceed to the answer.
As the temperature of a liquid/solid increases, its volume increases. Most liquids behave this way. But, water has a unique quality, above (almost) 4°C water behaves normally i.e its volume increases as the temperature increases. However, between 0°C and almost 4°C its volume decreases with rise in temperature( or increases with temperature drop, thus making it less dense)-this is anomalous behaviour of water.
Say the water at the surface is at 12°C and its cooling down. Now, as the temperature decreases, its volume decreases and density increases. As the surface water reaches about 4°C, it becomes more dense and "sinks" to the bottom allowing the less dense water to surface up. As temperature falls below 4°C, surface water becomes lighter( less dense) compared to the water below and floats until it freezes. Once frozen, the ice insulates the water at the bottom from cooling so its temperature is maintained between 0 and almost 4°C, keeping it from freezing.

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