Question

Which of the following reactions are disproportionation reaction?
a)\(2Cu^{+}\rightarrow Cu^{2+}+Cu^{0}\)
\(b)3MnO_4^{2-}+4H^{+} \rightarrow2MnO_4^{-}+MnO_2+2H_2O\)
\(c)2KMnO_4\frac{\Delta}{\rightarrow}K_2MnO_4+MnO_2+O_2\)
\(d)2MnO_4^{-}+3Mn^{2+}+2H_2O \rightarrow 5MnO_2+4H^\oplus\)
Select the correct option from the following:

• A. (a) and (b) only
• B. (a), (b) and (c)
• C. (a), (c) and (d)
• D. (a) and (d) only

Answer 1

The Correct Option is A

A disproportionation reaction is a specific type of redox reaction in which a single element is simultaneously oxidized and reduced. To identify which reactions are disproportionation reactions, let's analyze each option:

1. Reaction (a): \(2Cu^{+}\rightarrow Cu^{2+}+Cu^{0}\)

This is a disproportionation reaction because:

• The oxidation state of copper changes from +1 in Cu^+ to +2 in Cu^{2+} (oxidation).
• The oxidation state of the other copper changes from +1 in Cu^+ to 0 in Cu^{0} (reduction).

2. Reaction (b): \(3MnO_4^{2-}+4H^{+} \rightarrow2MnO_4^{-}+MnO_2+2H_2O\)

This reaction is also a disproportionation reaction:

• The oxidation state of manganese changes from +6 in MnO_4^{2-} to +7 in MnO_4^{-} (oxidation).
• The oxidation state of another manganese changes from +6 in MnO_4^{2-} to +4 in MnO_2 (reduction).

3. Reaction (c): \(2KMnO_4\frac{\Delta}{\rightarrow}K_2MnO_4+MnO_2+O_2\)

This is not a disproportionation reaction because the oxidation states of manganese in the compounds involved do not simultaneously increase and decrease; instead, it involves a thermal decomposition and oxidation process.

4. Reaction (d): \(2MnO_4^{-}+3Mn^{2+}+2H_2O \rightarrow 5MnO_2+4H^\oplus\)

This reaction involves redox changes but is not characterized as a disproportionation reaction as it involves separate species undergoing reduction and oxidation rather than a single element changing oxidation states in two directions within the same reaction.

Based on this analysis, the reactions that qualify as disproportionation reactions are (a) and (b). Therefore, the correct answer is (a) and (b) only.