Find out the most stable oxidised species.

Options

A. `Cr^(3+)`
B. `MnO_(4)^(-)`
C. `Cr_(2)O_(7)^(2-)`
D. `Mn^(2+)`

Explanation

To find the most stable oxidized species, we need to analyze the standard electrode potentials (E° values) for the oxidation reactions of different species. Here’s a step-by-step solution:

### Step 1: Identify the species and their oxidation states
We are considering the following species:
- Chromium (Cr) to Chromium(III) ion (Cr³⁺)
- Chromium(III) ion (Cr³⁺) to Dichromate ion (Cr₂O₇²⁻)
- Manganese(II) ion (Mn²⁺) to Permanganate ion (MnO₄⁻)

### Step 2: Write down the standard electrode potentials (E° values)
From the information provided:
- For the reaction: Cr → Cr³⁺, E° = +0.74 V
- For the reaction: Cr³⁺ → Cr₂O₇²⁻, E° = -1.33 V
- For the reaction: Mn²⁺ → MnO₄⁻, E° = -1.51 V

### Step 3: Analyze the stability of oxidized species
The stability of an oxidized species is generally indicated by its standard electrode potential. A higher (more positive) E° value indicates a more stable oxidized form.

1. **Cr to Cr³⁺**: The E° value is +0.74 V, indicating that Cr³⁺ is a stable oxidized species.
2. **Cr³⁺ to Cr₂O₇²⁻**: The E° value is -1.33 V, indicating that Cr₂O₇²⁻ is less stable compared to Cr³⁺.
3. **Mn²⁺ to MnO₄⁻**: The E° value is -1.51 V, indicating that MnO₄⁻ is also less stable compared to Mn²⁺.

### Step 4: Conclusion
Based on the E° values, the most stable oxidized species among the ones considered is **Cr³⁺** because it has the highest positive electrode potential (+0.74 V) compared to the other oxidized forms (Cr₂O₇²⁻ and MnO₄⁻).

### Final Answer
The most stable oxidized species is **Cr³⁺**.

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