Which reaction does not represent auto redox or disproptionation?

Options

A. `Cl_(2)+OH^(-) to Cl^(-)+ClO_(3)^(-)+H_(2)O`
B. `2H_(2)O_(2) to H_(2)O_(2)`
C. `2Cu^(+) to Cu^(2+)+Cu`
D. `(NH_(4))_(2)Cr_(2)O_(7) to N_(2)+Cr_(2)O_(3)+4H_(2)O`

Answer

To determine which reaction does not represent auto-redox or disproportionation, we need to understand the definitions of these terms:

1. **Auto-redox Reaction**: A reaction in which a single element undergoes both oxidation and reduction, meaning it loses and gains electrons simultaneously.
2. **Disproportionation Reaction**: A specific type of auto-redox reaction where a single substance is both oxidized and reduced to form two different products.

Now, let's analyze the reactions provided in the question step-by-step:

### Step 1: Identify the Reactions
We need to examine the reactions given in the options to see if they involve a single element being oxidized and reduced.

### Step 2: Analyze Each Reaction
1. **Chlorine Reaction**:
- Chlorine (Cl) goes from an oxidation state of 0 to -1 (reduction) and +5 (oxidation).
- This is a disproportionation reaction because chlorine is both oxidized and reduced.

2. **Oxygen Reaction**:
- In the reaction involving O2, oxygen goes from -1 to -2 (reduction) and -1 to 0 (oxidation).
- This is also a disproportionation reaction.

3. **Copper Reaction**:
- Copper goes from +1 to +2 (oxidation) and +2 to +1 (reduction).
- This is a redox reaction and also qualifies as disproportionation.

4. **Chromium Reaction**:
- Chromium goes from +6 to +3 (reduction) but does not have another component to oxidize itself.
- This does not represent a disproportionation reaction since it only involves reduction without simultaneous oxidation.

5. **Nitrogen Reaction**:
- Nitrogen in NH4+ goes from -3 to 0 (oxidation) without a corresponding reduction.
- This is a redox reaction but not a disproportionation reaction.

### Step 3: Conclusion
Based on the analysis, the reaction that does not represent auto-redox or disproportionation is the **chromium reaction**.

### Final Answer:
The reaction involving chromium does not represent auto-redox or disproportionation.

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