# How do you determine the oxidation state of metal ions?

Well, for ${M}^{2 +}$ and ${M}^{3 +}$ it's easy, we have $I I +$ and $I I I +$ oxidation states.
For complex ions such as $M n {O}_{4}^{-}$ and $C {r}_{2} {O}_{7}^{2 -}$ you have to do a little more work, but most of it is routine. Oxygen, in all its oxides, assumes an oxidation state of $- I I$. Thus the oxidation state of the metal in these oxides is the Group oxidation number, i.e. the maximum oxidation numbers, $M n \left(V I I +\right)$, and $C r \left(V I +\right)$. Are you clear on how these designations were obtained?
Can you tell me the metal oxidation states in: $M n {O}_{2}$; $Z r C {l}_{4}$; $P t C {l}_{4}$; $F {e}_{2} {O}_{3}$; $P d {\left(P P {h}_{3}\right)}_{4}$; and ${\left[F e {\left(C \equiv N\right)}_{6}\right]}^{3 -}$?