Using the standard electrode potential, find out the pair between which redox reaction is not feasible.
`E^(θ)` values : `Fe^(3+)//Fe^(2+)=0.77, I_(2)//I^(-)=+0.54`,
`Cu^(2+)//Cu=+0.34, Ag^(+)//Ag=+0.80V`

Options

A. `Fe^(3+)` and `I^(-)`
B. `Ag^(+)` and `Cu`
C. `Fe^(3+)` and `Cu`
D. `Ag` and `Fe^(3+)`

Answer

d

Explanation

(a) `2Fe^(3+)+2e^(-)to2Fe^(2+),E^(@)=+0.77V`
`2I^(-)toI_(2)+2e^(-), E^(@)=-0.54V" "`(Sign of `E^(@)` is reversed)
`2Fe^(3+)+2I^(-)to2Fe^(2+)+I_(2), E_("cell")^(@) = +0.23V`
This reaction is feasible since `E_("cell")^(@)` is positive.
(b) `CutoCu^(2+)+2e^(-), E^(@)=-0.34V" "`(Sign of `E^(@)` has been reversed)
`2Ag^(+)+2e^(-)to2Ag, E^(@)=+0.80V`
`Cu+2Ag^(+)to2Cu^(2+)+2Ag, E^(@)=+0.46V`
this reaction is feasible since `E_("cell")^(@)` is positive.
(c ) `{:(2Fe^(3+)+2e^(-)to2Fe^(2+),E^(@)=+0.77V),(CutoCu^(2+)+2e^(-),E^(@)=-0.34V):}/(2Fe^(3+)+Cuto2Fe^(2+)+Cu^(2+),E^(@)=+0.43V)" "`(sign of `E^(@)` is reversed)
This reaction is feasible since `E_("cell")^(@)` is positive.
(d) `Ag toAg^(+)+e^(-),E^(@)=-0.80V" "`(sign of `E^(@)` is reversed)
`Fe^(3+)+e^(-)toFe^(2+),E^(@)=+0.77V`
`Ag+Fe^(3+)toAg^(+)+Fe^(2+),E^(@)=-0.03V`
This reaction is not feasible since `E_("cell")^(@)` is negative