Iron (Fe) can exhibit different oxidation states in chemical compounds, resulting in different formulae:

Iron (Fe) is in its elemental state.Iron oxide (FeO) is a compound where iron is in the +2 oxidation state.Iron(II) chloride (FeCl2) is a compound where iron is in the +2 oxidation state.Iron(II) hydroxide (Fe(OH)2) is a compound where iron is in the +2 oxidation state.Iron(II) nitrate (Fe(NO3)2) is a compound where iron is in the +2 oxidation state.