$\mathop {KCl{O_3}}\limits^{ + 1 + 5 - 2} {\mkern 1mu} + \mathop {{H_2}{C_2}{O_4}}\limits^{ + 1 + 3 - 2} {\mkern 1mu} + \mathop {{H_2}S{O_4}}\limits^{ + 1 + 6 - 2} {\mkern 1mu} $$ \rightarrow \mathop {{K_2}S{O_4}}\limits^{ + 1 + 6 - 2} {\mkern 1mu} + \mathop {KCl}\limits^{ + 1 - 1} {\mkern 1mu} + \mathop {C{O_2}}\limits^{ + 4 - 2} {\mkern 1mu} + \mathop {{H_2}O}\limits^{ + 4 - 2} {\mkern 1mu} $
Thus, $Cl$ is the element which undergoes maximum change in the oxidation state.
$I.\,C{r_2}{O_7}^{2 - }\, + \,2O{H^ - }\, \to \,Cr{O_4}^{2 - }\, + \,{H_2}O$
$II.\,Zn\, + \,CuS{O_4}\, \to \,ZnS{O_4}\, + \,Cu$
$III.\,2Mn{O_4}^ - \, + \,3M{n^{2 + }}\, + \,4O{H^ - }\, \to \,5Mn{O_2}\, + \,2{H_2}O$
$IV.\,2C{u^ + }\, \to \,Cu\, + \,C{u^{2 + }}$