Which one of the following is an example of disproportionation reaction?

Question

$$\begin {array} {1 1}(a)\;3Cl_2(g)+60H^- (aq) \to CIO_3^-(aq) +5CL^{-1} (aq)+3H_2O(l) \\ (b)\;Ag^{2+}(aq)+Ag(s) \to 2Ag^+(aq) \\ (c)\;Zn(s)+CuSO_4(aq)\to Cu(s)+ZnSO_4(aq) \\ (d)\;2KCIO_3(s) \to 2KCI(s)+30_2(g)\end {array}$$