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

Options

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

Explanation

To determine the pair between which a redox reaction is not feasible using the standard electrode potentials, we can follow these steps:

### Step 1: Understand the standard electrode potentials
We have the following standard electrode potentials:
- \( E^\circ \) for \( Fe^{3+} // Fe^{2+} = +0.77 \, V \)
- \( E^\circ \) for \( I_2 // I^- = +0.54 \, V \)
- \( E^\circ \) for \( Cu^{2+} // Cu = +0.34 \, V \)
- \( E^\circ \) for \( Ag^+ // Ag = +0.80 \, V \)

### Step 2: Identify the highest and lowest potentials
In a redox reaction, the species with the higher standard reduction potential will act as the oxidizing agent, while the species with the lower standard reduction potential will act as the reducing agent.

### Step 3: Compare the potentials
We can compare the potentials:
- \( Ag^+ \) has the highest potential at \( +0.80 \, V \).
- \( Fe^{3+} \) follows with \( +0.77 \, V \).
- \( I_2 \) is next with \( +0.54 \, V \).
- \( Cu^{2+} \) has the lowest potential at \( +0.34 \, V \).

### Step 4: Determine feasibility of reactions
For a redox reaction to be feasible, the difference in potentials must be significant enough to drive the reaction. If two species have very similar potentials, the reaction between them will not be favorable.

### Step 5: Identify the pair with similar potentials
Looking at the potentials:
- \( Ag^+ \) and \( Fe^{3+} \) have potentials of \( +0.80 \, V \) and \( +0.77 \, V \) respectively, which are quite close.
- The other pairs have larger differences in their potentials.

### Conclusion
The pair between which the redox reaction is not feasible is \( Ag^+ \) and \( Fe^{3+} \) because their standard electrode potentials are very close to each other, indicating that a redox reaction between them would not proceed effectively.

### Final Answer
The pair between which the redox reaction is not feasible is \( Ag^+ // Fe^{3+} \).

---