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 (i) `E_("cell")^0=E_(OP_(Fe^(2+)//Fe^(3+)))^0+E_(RP_(Sn^(2+)//Sn^(3+)))^0=-0.77+0.1`
`Fe^(2+)` oxidizes and `Sn^(4+)` reduces in change,
`E_("cell")^0=-0.67v,E_("cell")^0` is negative
`:.` (i) Is non-spontaneous change
For (ii) `E_("cell")^0=E_(OP_(Fe^(2+)//Fe^(3+))^0+E_(RP_(I_2//I^-))^0=-0.77+0.54=-0.23V`
`:.` (ii) Is non-spontaneous change
For (iii) `E_("cell")^0=E_(OP_(I_2//I^-))^0+E_(RP_(Sn^(4+)//Sn^(2+)))^0=-0.54+0.1=-0.44v`
`:.` (iii) Is non-spontaneous change
For (iv) `E_("cell")^0=E_(OP_(Sn^(4+)//Sn^(2+)))^0+E_(RP_(I2//I^-))^0=-0.1+0.54=+0.44V`
(iv) Is spontaneous change