Calculate the oxidation state of metal ion in:
i) `[Ag(CN)_(2)]^(-)`
ii) `[Ni(CO)_(4)]`
iii) `[Fe(CN)_(6)]^(3-)`

Explanation

i) `[Ag(CN)_(2)]^(-)] : x+2(-)=-1 or x=+1`
ii) `[Ag(CN)_(2)]^(-): x+4(0)=0` or x=0
iii) `[Fe(CN)_(6)]^(3-)` : `x+6(-1)=-3` or `x=+3`.