The reaction 3ClO^–_(aq) → ClO₃^–_(aq) + 2Cl^–_(aq) is an example of

$3\stackrel{+1}{\mathrm{Cl}}{\mathrm{O}}^{–}\left(\mathrm{aq}\right) \to \stackrel{+5}{\mathrm{Cl}}{\mathrm{O}}_3^{-}\left(\mathrm{aq}\right) + \stackrel{-1}{2{\mathrm{Cl}}^{–}}\left(\mathrm{aq}\right)$

Both reduction and oxidation of Cl happens in the given reaction. Hence, option-C is correct.