oxidation state

n. (Chemistry) oxidation number, number of electrons needed to restore an atom in a combining condition to its elemental form

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are represented by Arabic numerals and can be positive, negative, or zero. Thus, H+ would have an oxidation state of +1.
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Noun
1. the degree of oxidation of an atom or ion or molecule; for simple atoms or ions the oxidation number is equal to the ionic charge; "the oxidation number of hydrogen is +1 and of oxygen is -2"
(synonym) oxidation number
(hypernym) number

A convention for representing a charge of an atom embedded within a compound, if the compound were purely ionic. For example, H2O is a covalent compound; if it were ionic, the hydrogens would be H+ (oxidation number +1) and the oxygen would be O2- (oxidation number -2). Oxidation number rises for at least one atom in a compound that is oxidized ; oxidation number becomes smaller if the compound is reduced.