Question on Disproportionation

Which one among HClO, HClO₂, HClO₃ and HClO₄ does not undergo disproportionation?

Answer:

Disproportionation is the process in which an element undergoes both oxidation and reduction in a reaction. Moreover, an element can show a maximum oxidation state equal to its “group number” and a minimum oxidation state equal to its “group number – 8”. Among the oxyacids of chlorine given, in HClO₄ chlorine is in its highest oxidation state (+7). So, it cannot undergo further oxidation and hence HClO₄ cannot undergo dispropotionation.