Question

what expands on reducing its temperature below ____________ ℃

Answer 1

Water expands on reducing it's temperature below 4 degree Celsius.

This is called an anamolous expansion of water.......

Answer 2

Water expands on reducing its temperature below 4 degree Celsius.

EXPLANATION:

The 'expansion of water' is unusual because most liquids expand on cooling.  At 4 degrees, water has the 'highest density' and water will expand whether it is heated or cooled beyond this temperature.

Below the temperature of 4 degrees, water turns to ice and therefore expand. When water starts getting colder, the 'molecules' move together and take up more 'space' and therefore expand.