Which of the following reactions are disproportionation reactions?
(A) $\mathrm{Cu}^{+} \rightarrow \mathrm{Cu}^{2+}+\mathrm{Cu}$
(B) $3 \mathrm{MnO}_4^{2-}+4 \mathrm{H}^{+} \rightarrow 2 \mathrm{MnO}_4^{-}+\mathrm{MnO}_2+2 \mathrm{H}_2 \mathrm{O}$
(C) $2 \mathrm{KMnO}_4 \rightarrow \mathrm{~K}_2 \mathrm{MnO}_4+\mathrm{MnO}_2+\mathrm{O}_2 \mid$
(D) $2 \mathrm{MnO}_4^{-}+3 \mathrm{Mn}^{2+}+2 \mathrm{H}_2 \mathrm{O} \rightarrow 5 \mathrm{MnO}_2+4 \mathrm{H}^{+}$
Choose the correct answer from the options given below:
