Which of the following reactions are disproportionation reactions?

(a) Cu+ → Cu2+ + Cu


(b) 3MnO42– + 4H+→ 2MnO4– + MnO2 + 2H2O


(c) 2KMnO4→ K2MnO4 + MnO2 + O2


(d) 2MnO4– + 3Mn2+ + 2H2O → 5MnO2 + 4H+


A disproportionation reaction takes place when a molecule is transformed into two products, one of higher oxidation state and another of lower oxidation state than the reactant molecule. It is a typical reduction reaction.

Cu+→ Cu2+ + Cu


In this reaction, Cu+ with oxidation state +1 forms Cu2+(+2 higher oxidation state) and Cu ( 0 lower oxidation state)


Similarly in this reaction,


3MnO42– + 4H+→ 2MnO4– + MnO2 + 2H2O


MnO42– with oxidation state +6 forms two products MnO4– with +7(higher oxidation state) and MnO2 with +4(lower oxidation state)

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