What is the oxidation number of the metal atom in the following ions?
`(i) [Fe(CN)_(6)]^(3) ,(ii) MnO_(4), (iii) [Cr(H_(2)O)_(6)]^(3^(+)`

Explanation

`(i) Fe in [Fe(CN)_(6)]^(3^(+))ion`
In this ion, the oxidation number of CN ions is -1 Let the oxidation number of Fe ber x. write the oxidation number of Fe above its symbol and that of `CN^(-)` ion above its formula.
`overset(x)Feoverset(-1)(CN)_(6)`
Caclulate the oxidation num,bners of all the species
`x+6(-1)=x-6`
Since `[Fe(CN)_(6)]^(3)` is an anion the sum of the oxidation j number must be -3
`x-6=-3 or x=+3.`
`(ii) Mn in MnO_(4)` ion
Let the oxidation number of atoms above their symbols
`overset(x)Mn overset(-2)O_(4)`
Calculate the oxidation number of all the atoms
since `[MnO_(4))]` is an anion , the sum of the oxidation numbers must bve-1
`therefore x-8=-1 orx=-21+8=+7`
`Cr in [Cr(H_(2)O)_(6)]^(3+) ion`
As `H_(2)O` is a neurtral molecule its oxidation number is taken as 0
Write the oxidation number of `Cr` above its symbol and that of `H_(2)O` above its formula.
`overset(x)Croverset(O)(H_(2))O_(6)`
Since `[Cr(H_(2)O)_(6)]^(3+)` is an ion , the sum of the oxidation numbers must be+3
`x=+3`