noun
oxidation number
Chemistry term for the hypothetical charge of an atom if all bonds were ionic. Used in redox reactions and nomenclature.
過マンガン酸カリウムでは、マンガンの酸化数は+7です。
In potassium permanganate, the oxidation number of manganese is +7.
価数 (valence) is a broader concept; 酸化数 is a specific formalism used in redox chemistry.
Compound of 酸化 (oxidation) and 数 (number). A straightforward calque of the English term 'oxidation number'.