Which of the following reactions are disproportionation reactions?
a. $2Cu^{+}\rightarrow Cu^{2+}+Cu$
b. $3MnO_{4}^{2-}+4H^{+}\rightarrow2MnO_{4}^{-}+ MnO_{2}+2H_{2}O$
c. $2KMnO_{4}\rightarrow K_{2}MnO_{4}+MnO_{2}+ O_{2}$
d. $10I^{-}+2MnO_{4}^{-}+16H^{+}\rightarrow2Mn^{2+} +8H_{2}O+5I_{2}$

Question

Which of the following reactions are disproportionation reactions? 
a. $2Cu^{+}\rightarrow Cu^{2+}+Cu$ 
b. $3MnO_{4}^{2-}+4H^{+}\rightarrow2MnO_{4}^{-}+ MnO_{2}+2H_{2}O$ 
c. $2KMnO_{4}\rightarrow K_{2}MnO_{4}+MnO_{2}+ O_{2}$ 
d. $10I^{-}+2MnO_{4}^{-}+16H^{+}\rightarrow2Mn^{2+} +8H_{2}O+5I_{2}$

Accepted Answer

To determine which reactions are disproportionation reactions, we need to understand what a disproportionation reaction is. A disproportionation reaction is a specific type of redox reaction in which a single substance is simultaneously oxidized and reduced, forming two different products.

Let's analyze each reaction:

a. $2Cu^{+} \rightarrow Cu^{2+} + Cu$

In this reaction, the copper ion $Cu^{+}$ is both oxidized and reduced. One $Cu^{+}$ ion is oxidized to $Cu^{2+}$, and another $Cu^{+}$ ion is reduced to metallic copper $Cu$. This is a classic example of a disproportionation reaction.

b. $3MnO_{4}^{2-} + 4H^{+} \rightarrow 2MnO_{4}^{-} + MnO_{2} + 2H_{2}O$

In this reaction, the manganese in $MnO_{4}^{2-}$ is both oxidized and reduced. Some of the manganese is oxidized to $MnO_{4}^{-}$, while some is reduced to $MnO_{2}$. This fits the definition of a disproportionation reaction.

c. $2KMnO_{4} \rightarrow K_{2}MnO_{4} + MnO_{2} + O_{2}$

In this reaction, $KMnO_{4}$ is not undergoing a disproportionation reaction. Instead, it is decomposing into different products without a single species being both oxidized and reduced. Therefore, this is not a disproportionation reaction.

d. $10I^{-} + 2MnO_{4}^{-} + 16H^{+} \rightarrow 2Mn^{2+} + 8H_{2}O + 5I_{2}$

In this reaction, the iodide ions $I^{-}$ are oxidized to iodine $I_{2}$, and the permanganate ions $MnO_{4}^{-}$ are reduced to $Mn^{2+}$. There is no single species undergoing both oxidation and reduction, so this is not a disproportionation reaction.

Based on the analysis above, reactions a and b are disproportionation reactions. Therefore, Option 4 (a, b) is the correct answer.

Explanation of why other options are incorrect:

1. Option 1 (c, d): Neither reaction c nor d is a disproportionation reaction, as explained above.
2. Option 2 (a, c): While reaction a is a disproportionation reaction, reaction c is not.
3. Option 3 (b, c): Reaction b is a disproportionation reaction, but reaction c is not.

Thus, the correct answer is Option 4, which includes reactions a and b as disproportionation reactions.