If ice is solid,which has low density how can it float on water?

Water has highest density at 4 C.  Below this temperature, the density of water goes on decreasing. Te reason is as follows:

 

A water molecule is made from one oxygen atom and two hydrogen atoms, strongly joined to each other with covalent bonds. Water molecules are also attracted to each other by weaker chemical bonds i.e. hydrogen bonds between the positively-charged hydrogen atoms and the negatively-charged oxygen atoms of neighbouring water molecules.

 

As water cools below 4 C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart.

The crystal lattice produced is called as ‘Ice’. It floats on water because it is about 9% less dense than liquid water or say, ice takes up about 9% more space than water. The heavier liquid water displaces the lighter ice, hence ice floats on water.