Which of the following reactions are
disproportionation reaction?
(a )`` 2Cu^+ \longrightarrow`` ``Cu^{2+} + Cu^0``
(b)``3MnO_4^{2-} + 4H^+ \longrightarrow`` ``2MnO_4^- + MnO_2 + 2H_2O``
(c)\begin{aligned}
& \ce{$2KMnO_4 $ ->[\ce{\triangle}] $K_2MnO_4 + MnO_2 + 0_2$}
\end{aligned}
(d)``2MnO_4 ^- + 3Mn^{2+} + 2H_2O \longrightarrow`` ``5MnO_2 + 4H^+``
Select the correct option from the following
(1) (a) and (b) only
(2) (a), (b) and (c)
(3) (a), (c) and (d)
(4) (a) and (d) only