The oxidation state of a central metal atom in a coordination entity is defined as the charge it would bear if all the ligands were removed along with the electron pairs that were shared with the central atom. In naming a complex, it is represented by a Roman numeral. For e.g., in coordination entity [Fe (CN)6]4- the oxidation state of iron is represented as (II). In [Fe (CN)6]4- , let the oxidation number of iron is x
The net charge = – 4
x + 6 (-1) = – 4
x – 6 = – 4
x = 6 – 4
= +2
So, iron oxidation state (II).