Select the spontaneous rreactions from the changes given below
`a. Sn^(4+)+2Fe^(2+)rarrSn^(2+)+2Fe^(3+)`
`b. 2Fe^(2+)=I_(2)rarr2Fe^(3+)+2I^(c-)`
`c. Sn^(4+)+2I^(c-)rarr Sn^(2+)+I_(2)`
`d. Sn^(2+)+I_(2) rarr Sn^(4+)+2I^(c-)`

Explanation

For `(a) Sn^(4+)` reduces to `Sn^(2+)` and `Fe^(2+)` oxidizes to `Fe^(3+)` .
`:. E^(c-)._(cell)=E^(c-)._(cell)+E^(c-)._(o x i d)`
`=E^(c-)._(Sn^(4+)|Sn^(2+))+E^(c-)._(Fe^(2+)|Fe^(3+))`
`=0.1 V-0.77V=-0.67V`
Hence, `E^(c-)._(cell)` is negative and the cell is non`-` spontaneous.
For `(b), I_(2)` reduces to `2I^(c-)` and `Fe^(2+)` oxidizes to `Fe^(3+)`
`:. E^(c-)._(cell)=E^(c-)._(red)+E^(c-)._(o x i d)`
`=E^(c-)._(I_(2)|2I^(c-))+E^(c-)._(Fe^(2+)|Fe^(3+))`
`=0.54V-0.77V=-0.23V`
Hence, `E^(c-)._(cell)` is negative and the cell is non`-` spontaneous.
For `(c),Sn^(4+)` reduces to `Sn^(2+)` and `EI^(c-)` oxides to `I_(2)`.
`:. E^(c-)._(cell)=E^(c-)._(red)+E^(c-)._(o x i d)`
`=E^(c-)._(Sn^(4+)|Sn^(2+))+E^(c-)._(2I^(c-)|I_(2))`
`=0.1V-0.54V=-0.44V`
Hence , `E^(c-)._(cell)` is negative and the cell is non`-` spontaneous.
For `(d),I_(2)` reduces to `2I^(c-)` and `Sn^(2+)` oxides to `Sn^(4+)`.
`:. E^(c-)._(cell)=E^(c-)._(red)+E^(c-)._(o x i d)`
`=E^(c-)._(I_(2)|2I^(c-))+E^(c-)._(Sn^(2+)|Sn^(4+))`
`=0.54V-0.1V=0.44V`
Hence,` E^(c-)._(cell)` is positive and the cell is spontaneous.