Which of the following reactions are disproportionation reactions?

A. \(2Cu^+ \longrightarrow Cu^{2+} + Cu\)

B. \(3MnO_4^{2-} + 4H^+ \longrightarrow 2MnO_4^- + MnO_2 + 2H_2O\)

C. \(2KMnO_4 \longrightarrow K_2MNO_4 + MnO_2 + O_2\)

D. \(2MnO_4^- + 3Mn^{2+} + 2H_2O \longrightarrow 5MnO_2 + 4H^+\)

Choose the correct answer from the options given below:

A, B, C

The correct answer is option 2. A, B, C.

A disproportionation reaction is a type of redox reaction where a single substance is simultaneously oxidized and reduced. This means that the same element in a single reactant undergoes both oxidation (loses electrons) and reduction (gains electrons).

 A. \(2Cu^+ \longrightarrow Cu^{2+} + Cu\)

Reaction Analysis:

Initial Species: \(Cu^+\) (Copper(I) ion).

Products: \(Cu^{2+}\) (Copper(II) ion) and \(Cu\) (Copper metal).

Oxidation and Reduction:

Oxidation: \(Cu^+\) is oxidized to \(Cu^{2+}\) (loss of one electron).

Reduction: \(Cu^+\) is reduced to \(Cu\) (gain of one electron).

In this reaction, \(Cu^+\) is undergoing both oxidation and reduction. Hence, it is a disproportionation reaction.

B. \(3MnO_4^{2-} + 4H^+ \longrightarrow 2MnO_4^- + MnO_2 + 2H_2O\)

Reaction Analysis:

Initial Species: \(MnO_4^{2-}\) (Manganese(II) oxoanions).

Products: \(MnO_4^-\) (Manganese(VII) oxoanions) and \(MnO_2\) (Manganese(IV) oxide).

Oxidation and Reduction:

Oxidation: Manganese in \(MnO_4^{2-}\) is oxidized to \(MnO_4^-\) (increasing oxidation state from +4 to +7).

Reduction: Manganese in \(MnO_4^{2-}\) is reduced to \(MnO_2\) (decreasing oxidation state from +4 to +4).

In this reaction, \(Mn\) from \(MnO_4^{2-}\) undergoes both oxidation (to \(MnO_4^-\)) and reduction (to \(MnO_2\)). Therefore, it is a disproportionation reaction.

C. \(2KMnO_4 \longrightarrow K_2MnO_4 + MnO_2 + O_2\)

Reaction Analysis:

Initial Species: \(KMnO_4\) (Potassium permanganate).

Products: \(K_2MnO_4\) (Potassium manganate), \(MnO_2\) (Manganese(IV) oxide), and \(O_2\) (Oxygen gas).

Oxidation and Reduction:

Oxidation: Manganese in \(KMnO_4\) is oxidized to \(K_2MnO_4\) (oxidation state changes from +7 in \(KMnO_4\) to +6 in \(K_2MnO_4\)).

Reduction: Manganese in \(KMnO_4\) is reduced to \(MnO_2\) (oxidation state changes from +7 in \(KMnO_4\) to +4 in \(MnO_2\)).

Here, \(Mn\) in \(KMnO_4\) undergoes both oxidation (to \(K_2MnO_4\)) and reduction (to \(MnO_2\)). Hence, this reaction is a disproportionation reaction.

D. \(2MnO_4^- + 3Mn^{2+} + 2H_2O \longrightarrow 5MnO_2 + 4H^+\)

Reaction Analysis:

Initial Species: \(MnO_4^-\) (Permanganate ion) and \(Mn^{2+}\) (Manganese(II) ion).

Products: \(MnO_2\) (Manganese(IV) oxide).

Oxidation and Reduction:

Reduction: Manganese in \(MnO_4^-\) is reduced to \(MnO_2\) (reduction from +7 to +4).

No Oxidation: \(Mn^{2+}\) is not oxidized; it is only involved in the reaction to produce \(MnO_2\).

In this reaction, \(Mn\) in \(MnO_4^-\) is reduced, but \(Mn^{2+}\) is not oxidized. There is no simultaneous oxidation and reduction of the same species. Therefore, this is not a disproportionation reaction.

Conclusion

Thus, the reactions that are disproportionation reactions are:

A. \(2Cu^+ \longrightarrow Cu^{2+} + Cu\)

B. \(3MnO_4^{2-} + 4H^+ \longrightarrow 2MnO_4^- + MnO_2 + 2H_2O\)

C. \(2KMnO_4 \longrightarrow K_2MnO_4 + MnO_2 + O_2\)

So the correct answer is indeed: Option 2: A, B, C.