These are different chemical compounds that contain iron $Fe$ in various oxidation states and in combination with different elements:

Fe: Iron in its elemental formFeO: Iron oxide, with iron in the +2 oxidation stateFeCl2: Iron chloride, with iron in the +2 oxidation stateFe$OH$2: Iron hydroxide, with iron in the +2 oxidation stateFeSO4: Iron sulfate, with iron in the +2 oxidation stateFe$NO3$2: Iron nitrate, with iron in the +2 oxidation state