Using the standard electrode potential, find out the pair between which redox reaction is not feasible.

Evalues:Fe3+/Fe2+=+0.77;I2/I-=+0.54;
Cu2+/Cu=+0.34;Ag+/Ag=+0.80V

1. Fe3+ and I-

2. Ag+ and Cu

3. Fe3+ and Cu

4. Ag and Fe3+

Hint: Ecello value must be positive
 
Calculate the value of Ecello for every options as follows:
(1)
 
2Fe3++2e-2Fe2+;E°=+0.77V
2I-I2+2e-;E°=-0.54V(signofE°isreversed)
2Fe3++2I-2Fe2++I2;E°cell+0.23V
This reaction is feasible since E°cell is positive.
 
(2)
 
CuCu2++2e-;E°=-0.34V(signofE°hasbeenreversed)
2Ag++2e-2Ag;E°=+0.80V
Cu+2Ag+2Cu2+2Ag;E°=+0.46V
This reaction is feasible since E°cell is positive.
 
(3)
 
2Fe3++2e-2Fe2+;E°=+0.77V
CuCu2++2e-;E°=-0.34V2Fe3++Cu2Fe2++Cu2+;E°=+0.43V(signofE°isreversed)
This reaction is feasible since E°cell is positive.
 
(4)
 
AgAg++e-;E°=-0.80V(signofE°isreversed)
Fe3++e-Fe2+;E°=+0.77V
Ag+Fe3+Ag++Fe2+;E°=-0.03V
This reaction is not feasible since E°cell is negative