We have to know the number of molecules present in 500 g of water.
The answer is: zero molecules present in 500g of water.
Water molecule is H₂O. In water molecule, nitrogen molecule can not be present. Molecular mass of water is 18 g. MOlecular mass of nitrogen molecule is 28 g.
500 g water contains 500/18 number of moles= 27.77 moles of water molecules which contains 27.77 X 6.023 X 10²³ number of water molecules.
There is no existence of N₂ molecule.