Question

Ice floats on water because:
A. density of ice is less than density of water
B. density is same as that of water
C. density of ice is greater than water
D. None of the above

Answer 1

Hint: In liquid state, water molecules are held together by weak hydrogen bonds whereas, in solid form the water molecules are held together by strong hydrogen bonds.

Complete step by step answer:
We know that lesser the density, lighter is the object that means ice has less density than water as we have observed it when we are dipping an ice cube in liquid water, the ice cube floats over the surface. Let us see how this is happening –
Ice is solid form of $H_{2}O$ and water is liquid form of $H_{2}O$.
In liquid state water molecules are very disordered due to their mobility and weak hydrogen bonds between them. But in solid state water molecules have less mobility due strong hydrogen bonding between them.
Ice has a highly ordered three-dimensional hexagonal (hydrogen bonded) structure. X-rays show that each oxygen atom is surrounded tetrahedrally by four other oxygen atoms at a distance of$276pm$.
Hydrogen bonding gives ice a rather open type structure with wide holes whereas; structure of water didn’t give any free space in the molecular structure.
This gapping in the structure reduces density and increases volume.
Hence, the density of ice is less than that of water and therefore it floats on water.
The density of water is maximum at 4 degree Celsius. This abnormal behaviour of water helps in survival of marine animals. This is a god’s gift because if water starts freezing at 0 degree Celsius the marine animals also get freezed.

Therefore, option A is correct.

Note: Generally, the density of solid form is higher than liquid form. Thus, water shows an abnormal behaviour that is ice has lesser density than water due that behaviour.