The `E^(o)""_(M^(3+)//M^(2+))` values for Cr, Mn, Fe and Co are `–0.41, +1.57,+ 0.77 and + 1.97`V respectively. For which one of these metals the change in oxidation state from +2 to +3 is the easiest?

Options

A. Co
B. Mn
C. Fe
D. Cr

Answer

To determine which metal has the easiest change in oxidation state from +2 to +3, we need to analyze the given standard reduction potentials for the metals Cr, Mn, Fe, and Co.

### Step-by-step Solution:

1. **Understanding the Reduction Potentials**: The given standard reduction potentials (E°) for the metals are:
- Cr³⁺/Cr²⁺: -0.41 V
- Mn³⁺/Mn²⁺: +1.57 V
- Fe³⁺/Fe²⁺: +0.77 V
- Co³⁺/Co²⁺: +1.97 V

2. **Identifying the Reaction**: The question asks for the change from +2 to +3 oxidation state, which corresponds to the oxidation process:
\[ M^{2+} \rightarrow M^{3+} + e^- \]
This is the reverse of the reduction process.

3. **Reversing the Potentials**: To find the oxidation potential, we reverse the sign of the reduction potentials:
- For Cr: E° = +0.41 V
- For Mn: E° = -1.57 V
- For Fe: E° = -0.77 V
- For Co: E° = -1.97 V

4. **Comparing Oxidation Potentials**: Now we compare the oxidation potentials:
- Cr: +0.41 V
- Mn: -1.57 V
- Fe: -0.77 V
- Co: -1.97 V

5. **Determining the Easiest Oxidation**: The metal with the highest oxidation potential will have the easiest transition from +2 to +3. Here, Cr has the highest oxidation potential of +0.41 V.

6. **Conclusion**: Therefore, the change in oxidation state from +2 to +3 is easiest for Chromium (Cr).

### Final Answer:
The metal for which the change in oxidation state from +2 to +3 is the easiest is **Chromium (Cr)**.