Stock system

:  a system in chemical nomenclature and notation of indicating the oxidation state of the significant element in a compound or ion by means of a Roman numeral that is used in parentheses after the name or part of the name designating this element and ending invariably in -ate in the case of an anion and that is placed above and to the right of the symbol for this element according to the Stock system nitrous oxide is named nitrogen (I) oxide, ferrosoferric oxide Fe₃O₄ is iron (II, III) oxide Fe^IIFe^III₂O₄, and potassium manganite is potassium manganate (IV) K₂Mn^IVO₃