Complex sentence: In chemistry the term is reserved for iron with an oxidation number of +3, denoted iron (III) or Fe 3 +, whereas ferrous indicates that it has oxidation number of +2 and is denoted iron (II) or Fe 2 +.
Split into simpler sentences: In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron (III) or Fe 3 +. Ferrous refers to iron with oxidation number of +2, denoted iron (II) or Fe 2 +.