Vanadium oxidation states. Vanadium can exist in four adjacent oxidation states (2-5) that produce solutions of different colours. Here left test tube contains solution of ammonium metavanadate (NH4VO3) where vanadium is in +5 oxidation state ((VO3)-). Next solutions (left to right) were obtained by reducing ammonium metavanadate using zinc amalgam as a catalyst: vanadium (IV) ((VO)2+, blue), vanadium (III) (V3+, green) and vanadium (II) (V2+, purple).