Which of the following is an example of disproportionation reaction?

Options

A. `2CuBrtoCuBr_(2)+Cu`
B. `KMnO_(4)toK_(2)MnO_(4)+MnO_(2)+O_(2)`
C. `MnO_(4)^(-)toKMnO_(2)+Mn^(2+)`
D. `Cl^(-)+ClO_(3)^(-)toCl_(2)`

Answer

To determine which of the given reactions is an example of a disproportionation reaction, we need to understand what a disproportionation reaction is. A disproportionation reaction is a type of redox reaction in which a single substance is both oxidized and reduced, resulting in the formation of two different products.

### Step-by-Step Solution:

1. **Identify the Reactions**: We need to analyze the provided options to see which one involves an element undergoing both oxidation and reduction.

2. **Analyze the First Reaction (CuBr2 + Cu)**:
- In CuBr2, the oxidation state of copper (Cu) is +2.
- In CuBr, the oxidation state of copper is +1.
- The elemental copper (Cu) has an oxidation state of 0.
- Here, Cu in CuBr2 is reduced from +2 to +1 (gaining an electron), and Cu is oxidized from 0 to +1 (losing an electron).
- Since one species (Cu) is both oxidized and reduced, this reaction is an example of disproportionation.

3. **Analyze the Second Reaction (KMnO4)**:
- In KMnO4, manganese (Mn) has an oxidation state of +7.
- In the products, Mn is in the +6 and +4 oxidation states.
- Here, Mn is only being reduced (the oxidation state is decreasing) and not oxidized. Therefore, this reaction does not qualify as a disproportionation reaction.

4. **Analyze the Third Reaction**:
- Similar to KMnO4, if we analyze the oxidation states of the species involved, we find that there is only a decrease in oxidation state (reduction) and no increase (oxidation).
- Thus, this reaction also does not qualify as a disproportionation reaction.

5. **Analyze the Fourth Reaction**:
- This reaction involves two ions combining to form one molecule, which does not involve any oxidation or reduction of the same element. Hence, it is not a disproportionation reaction.

6. **Conclusion**: Based on the analysis, the only reaction that shows an element undergoing both oxidation and reduction is the first one (CuBr2 + Cu). Therefore, the correct answer is option A.

### Final Answer:
The correct option is **A (CuBr2 + Cu)**, as it is the only example of a disproportionation reaction.

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