Under suitable conditions (for example on heating or in alkaline solution) which of the following chlorine oxoanions can undergo disproportionation?

Disproportionation needs a chlorine oxidation state that can go both up and down. $\mathrm{ClO}{}^{-}$ (+1), $\mathrm{ClO}{}_2{}^{-}$ (+3) and $\mathrm{ClO}{}_3{}^{-}$ (+5) are all intermediate states below the maximum of +7 and above -1. In $\mathrm{ClO}{}_4{}^{-}$ chlorine is already at +7 and can only be reduced.