What is the fraction of the mass of water due to neutrons?

Mass fraction:

• It is the mass of a species per unit mass of the mixture.

The fraction of the mass of water due to neutrons:

• Mass of neutron =$1\mathrm{amu}$.
• Mass of one water molecule = $18\mathrm{amu}.$
• The oxygen atom contains $8$ neutrons and the hydrogen atom has no neutrons.
• The mass of neutrons in one water molecule = $8\mathrm{amu}.$
• The fraction of the mass of water due to neutrons =$\frac{8}{18}=\frac{4}{9}=0.444$