1. Since `ClO_(2)` is reduced `[e^(-)+ClO_(2)rarrClO_(2)^(Ө)]`
so `O_(2)^(2-)` must be oxidised `[O_(2)^(2-)rarrO_(2)+2e^(-)]`
Oxidation: `O_(2)^(2-)rarrO_(2)+cancel(2e^(-))`
Reduction `{:(cancel(e^(-))+ClO_(2)rarrClO_(2)^(Ө)"]"xx2),(ulbar(O_(2)^(2)+2ClO_(2)rarrO_(2)+2ClO_(2)^(Ө))):}`
2. Since `IO_(3)^(Ө)` is oxidised `[IO_(3)^(Ө)rarrIO_(4)^(Ө)+2e^(-)]`
So `Cl_(2)` must be reduced `[Cl_(2)+2e^(-)rarr2Cl^(Ө)]`
Basic medium
Oxidation: `2overset(Ө)OH+H_(2)O+IO_(3)overset(Ө)rarrIO_(4)^(Ө)+cancel(2e^(-))+2H_(2)O`
Reduction: `{:(2e^(-)+Cl_(2)rarr2Cl^(Ө)),(ulbar(2overset(Ө)OH+IO_(3)^(Ө)+Cl_(2)rarrIO_(4)^(Ө)+@cl^(Ө)+H_(2)O)):}`
3. Since `Cu` is oxidised `[CurarrCu^(2+)+2e^(-)]`, so `NO_(3)^(Ө)` must be reduced `[e^(-)+NO_(3)^(Ө)rarrNO_(2)]`
Oxidation : `CurarrCu^(2)+cancel(2e^(-))`
Reduction: `{:(2H^(o+)+cancele^(-)+NO_(3)^(Ө)rarrNO_(2)+H_(2)O"]"xx2),(ulbar(Cu+4H^(o+)+2NO_(3)^(Ө)rarrCu^(2+)+2NO_(2)+2H_(2)O)):}`
4. Since `S^(2-)` is oxidised to `S(S^(2-)rarrS+2e^(-)"]"`, so `CrO_(4)^(2-)` is reduced to `Cr^(3+)(3e^(-)+CrO_(4)^(2-)rarrCr^(3+))`
Oxidation: `S^(2-)rarrS+cancel(2e^(-))"]"xx3`
Reduction: `{:(8H^(o+)+cancel(3e^(-))+CrO_(4)^(2-)rarrCr^(3+)+4H_(2)O"]"xx2),(ulbar(3S^(2-)+16H^(o+)+2CrO_(4)^(2-)rarr3S+2Cr^(3+)+8H_(2)O)):}`
Add, `4K^(o+)` and `5SO_(4)^(2-)` to both sides.
The net redox reaction is
`3H_(2)S+2K_(2)CrO_(4)+5H_(2)SO_(4)rarr3S+Cr_(2)(SO_(4))_(3)+2K_(2)SO_(4)+8H_(2)O`
5. Since `Fe^(2+)` is oxidised to `Fe^(3+) ( Fe^(2+)rarrFe^(3+)+e^(-))` , so `MnO_(4)^(Ө)` must be reduced to `Mn^(2+)`
`(5e^(-)+MnO_(4)^(Ө)rarrMn^(2+))`
Oxidation: `5Fe2^(+)rarr5Fe^(3+)+cancel(5e^(-))`
Reduction: `{:(8H^(o+)+cancel(5e^(-))+MnO_(4)^(Ө)rarrMn^(2+)+4H_(2)O),(ulbar(5Fe^(2+)+8H^(o+)+MnO_(4)^(Ө)rarr5fe^(3+)+Mn^(2+)+4H_(2)O)):}`
6. Since `HNO_(3)` is reduced to `N_(2)O[8e^(-)+2HNO_(3)rarrN_(2)O]`,
so `Zn` must be oxidised to `Zn^(2+)[ZnrarrZn^(2+)+2e^(-)]`
Oxidation `4Znrarr4Zn^(2+)+cancel(8e^(-))`
Reduction: `{:(8H^(o+)+cancel(8e^(-))+MnO_(4)^(Ө)rarrN_(2)O+5H_(2)),(ulbar(4Zn+8H^(o+)+2HNO_(3)rarr2Zn^(2+)+N_(2)O+5H_(2)O)):}`
or
`4Zn+10HNO_(3)rarr4Zn(NO_(3))_(2)+N_(2)O+5H_(2)O`
7. Since `NHO_(3)` is reduced to `NO[3e^(-)+HNO_(3)rarrNO]`, so `I^(Ө)` must be oxidised to `I_(2) [ 2I^(Ө)rarrI_(2)+2e^(-)]`
Oxidation: `cancel(3H^(o+))+cancel(3e^(-))+HNO_(3)rarrNO+2H_(2)O"]"xx2`
Reduction: `{:(2HIrarrI_(2)+cancel(2e^(-))+cancel(2H^(o+))"]"xx3),(ulbar(2HNO_(3)+6HIrarr3I_(2)+2NO+4H_(2)O)):}`.
