Question

what is the effect on density of water as its temperature increases from 0°c to 4°c

Answer 1

This is called as the anomalous behaviour of water

Answer 2

Usually,on heating other substances,their volume increases thus resulting in a decrease in density. But water is the only substance,whose density gradually increases between 0 degree celcius to 4 degree celcius. This effect is different so we call it as anamolous behaviour of water.