Volume occupied by one molecule of water  (density =1g cm−3) is :

The wt. of 6.023×1023 molecules of water is equal to g. mol. wt. of H2O i.e. 18 g∴ Volume occupied by 6.023×1023 molecules ofH2Od=1gcm−3=18g1gcm−3=18cm3Hence volume occupied by 1 molecule of H2O=186.023×1023≃3.0×10−23cm3.