Disproportionation is a specific type of redox reaction in which a species is simultaneously reduced and oxidised to form two different products. Electronic configuration of Cl is 1s22s22p23s23p64s1. It can exhibit maximum oxidation state of +7. All species can exhibit disproportionation reaction which simultaneously oxidise as well as reduce. In ClO4−,Cl cannot undergo oxidation as +7 is maximum oxidation state exhibited by chlorine.