Adjective
Of, pertaining to, designating, those compounds of manganese in which the element has a lower valence as contrasted with manganic compounds; as, manganous oxide.
Source: Webster's dictionaryThe net reaction of hydrogen peroxide and permanganate or manganese dioxide is manganous ion; however, until the peroxide is spent some manganous ions are reoxidized to make the reaction catalytic. Source: Internet