Tell you what - the more likely scenario is that iron reacts with oxygen to form 6.2g of Fe2O3. That's the rusting of iron; I don't know if you can "un-rust" iron back into pure iron and oxygen. So we'll go with this equation:
4Fe + 3O2 --> 2Fe2O3.
Iron (Fe) is our unknown. Okay, Fe2O3, which is iron(III) oxide, has a given mass of 6.2g, and according to the Periodic Table, it's molar mass, or grams per 1 mole, is 160g/mol (56+56+16+16+16). Do a 1-step molar conversion to get about 0.03875 moles. Apply this to the molar ratio of coefficients in the balanced equation: the ratio is 2:4, or 1:2, so you will double that to 0.0775 moles of iron. Now do a 1-step molar conversion with iron's Atomic Mass to get your grams of iron: 0.0775 moles x 56 grams per mole = 4.34 grams Fe.
