It's a general property of any substance that it expands on heating and contract on cooling but certain substances behave just different way at certain range of temperature. Water is an example.
Water expands on cooling from 4°C to 0°C or you can say water contracts on heating from 0°C to 4°C.
This unusual behaviour of water is called Anomalous expansion of water
Why is echo not heard in our living rooms? To hear echo, the minimum distance between the source and the reflector must be 17m. When this distance is more than 17m, the reflected sound can be distinguished from the original. As the length of our rooms is less than 17m, we don't hear echo.
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