4ClO^-_3(aq) → 3ClO^-_4(aq) + Cl^-_(aq) is an example of

$4\stackrel{+5}{\mathrm{Cl}}{\mathrm{O}}_3^{-}\left(\mathrm{aq}\right) \to 3\stackrel{+7}{\mathrm{Cl}}{\mathrm{O}}_4^{-}\left(\mathrm{aq}\right) + {\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)$

Here, 'Cl' undergoes both oxidation and reduction. Hence it is a Disproportionation reaction.