Balanced equation: 2Fe + 3H2O → Fe2O3 +3H2
Convert g to mols:
285/55.845 = 5.1034 mols
Mole ratio of Iron and Iron (III) Oxide: 2:1
5.1034/2 = 2.5517 mols
I would say its hydrogen, as it makes 51% of the cell constituents. This is followed by oxygen, which makes up 24% of the cell, and then carbon which is present as 11% of the total mass. Nitrogen makes up 4% of the cell, followed by other elements like phosphorous.