Oxidation reaction involves loss of electrons, and reduction reaction involves gain of electrons. The reaction in which a species disproportinates into two oxidation states ( lower and higher) is called disproportionation reaction.
Which of the following is not a dispropotional reaction?

Options

A. `overset(ө)OH+Br_(2)rarrBr^(ө)+BrO_(3)^(ө)`
B. `Cu_(2)O+2H^(o+)rarrCu+Cu^(2+)+H_(2)O`
C. `(CN)^(ө)rarrCO_(3)^(2-)+NO_(3)^(ө)`
D. `(CN)_(2)+2overset(ө)OHrarrCN^(ө)+CNO^(ө)+H_(2)O`

Explanation

To determine which of the given reactions is not a disproportionation reaction, we need to understand the concept of disproportionation reactions. A disproportionation reaction is a specific type of redox reaction where a single substance is both oxidized and reduced, resulting in the formation of two different products with different oxidation states.

Let's analyze each option step by step:

### Step 1: Identify the oxidation states in each reaction

1. **Br2 → Br⁻ + BrO3⁻**
- Oxidation state of Br in Br2 = 0
- Oxidation state of Br in Br⁻ = -1 (gaining an electron, reduction)
- Oxidation state of Br in BrO3⁻ = +5 (losing electrons, oxidation)
- This reaction involves both reduction and oxidation, hence it is a disproportionation reaction.

2. **2Cu⁺ → Cu + Cu²⁺**
- Oxidation state of Cu in Cu⁺ = +1
- Oxidation state of Cu in Cu = 0 (gaining an electron, reduction)
- Oxidation state of Cu in Cu²⁺ = +2 (losing electrons, oxidation)
- This reaction also involves both reduction and oxidation, hence it is a disproportionation reaction.

3. **CN⁻ → C + N**
- Oxidation state of C in CN⁻ = -1
- In this case, there is no change in oxidation state for both products (C and N) because CN⁻ is not splitting into two different oxidation states of the same element.
- Since there is no simultaneous oxidation and reduction, this is **not** a disproportionation reaction.

4. **3Fe²⁺ → 2Fe³⁺ + Fe**
- Oxidation state of Fe in Fe²⁺ = +2
- Oxidation state of Fe in Fe³⁺ = +3 (losing electrons, oxidation)
- Oxidation state of Fe in Fe = 0 (gaining electrons, reduction)
- This reaction involves both reduction and oxidation, hence it is a disproportionation reaction.

### Conclusion
Based on the analysis, the reaction that is **not** a disproportionation reaction is **option C: CN⁻ → C + N**.

### Final Answer
**The correct answer is option C.**