which of the following represent redox reactions?
I. `Cr_(2)O_(7)^(2-)+2overset(ө)OHrarr2CrO_(4)^(2-)+H_(2)O`
II. `Zn+CuSO_(4)rarrZnSO_(4)+Cu`
III. `MnO_(4)^(ө)+3Mn^(2+)+4overset(ө)OHrarr5MnO_(2)+2H_(2)O`
IV. `2Cu^(o+)rarrCu+Cu^(2+)`

Options

A. `I,II`
B. `I,III`
C. `III,IV`
D. `II,III,IV`

Explanation

To determine which of the given reactions represent redox reactions, we need to analyze the oxidation states of the elements involved in each reaction. A redox reaction involves the transfer of electrons, which results in changes in oxidation states of the reactants.

Let's analyze each reaction step by step:

### Step 1: Analyze Reaction I
**Reaction:** `Cr_(2)O_(7)^(2-) + 2OH^- → 2CrO_(4)^(2-) + H_(2)O`

- **Oxidation States:**
- In `Cr_(2)O_(7)^(2-)`, the oxidation state of Cr is +6.
- In `CrO_(4)^(2-)`, the oxidation state of Cr is also +6.

- **Conclusion:** The oxidation state of Cr does not change in this reaction. Therefore, there is no oxidation or reduction occurring. **This is NOT a redox reaction.**

### Step 2: Analyze Reaction II
**Reaction:** `Zn + CuSO_(4) → ZnSO_(4) + Cu`

- **Oxidation States:**
- In elemental Zn, the oxidation state is 0.
- In `CuSO_(4)`, the oxidation state of Cu is +2.
- In `ZnSO_(4)`, the oxidation state of Zn is +2.
- In elemental Cu, the oxidation state is 0.

- **Conclusion:** Zn is oxidized from 0 to +2, and Cu is reduced from +2 to 0. This indicates a transfer of electrons. **This is a redox reaction.**

### Step 3: Analyze Reaction III
**Reaction:** `MnO_(4)^(−) + 3Mn^(2+) + 4OH^- → 5MnO_(2) + 2H_(2)O`

- **Oxidation States:**
- In `MnO_(4)^(−)`, the oxidation state of Mn is +7.
- In `Mn^(2+)`, the oxidation state of Mn is +2.
- In `MnO_(2)`, the oxidation state of Mn is +4.

- **Conclusion:** Mn changes from +7 to +4 (reduction) and from +2 to +4 (oxidation). This indicates a transfer of electrons. **This is a redox reaction.**

### Step 4: Analyze Reaction IV
**Reaction:** `2Cu^(+1) → Cu + Cu^(2+)`

- **Oxidation States:**
- In `Cu^(+1)`, the oxidation state is +1.
- In elemental Cu, the oxidation state is 0.
- In `Cu^(2+)`, the oxidation state is +2.

- **Conclusion:** Cu is oxidized from +1 to +2 and reduced from +1 to 0. This indicates a transfer of electrons. **This is a redox reaction.**

### Final Conclusion
Based on the analysis:
- Reaction I: NOT a redox reaction
- Reaction II: IS a redox reaction
- Reaction III: IS a redox reaction
- Reaction IV: IS a redox reaction

**Correct Answer:** Reactions II, III, and IV represent redox reactions.