Rules for the Determination of Oxidation Numbers

To determine the oxidation number (ON) of an element the following rules are used  

The sum of the oxidation number of the atoms in a molecule ion must equal the charge on that molecule or ion, e.g. 

In covalent hydrides, hydrogen has an oxidation number of I, but in ionic hydrides such as NaH, hydrogen has an ON of — I. Fluorine generally has an oxidation number of — I and oxygen an ON of - II (or — I in peroxides such as H2O2). 

The use of formal oxidation numbers can also be applied to coordination complexes such as [Mn (OH2)6] and [Fe (OH2)6] or [Fe (OH2)6], where the water molecule is considered as a neutral species or written as 0 H 2, an overall neutral molecule. 

---