Disproportionation

This occurs when a reactant is both reduced and oxidised in the same reaction.

eg: H2O2 --> H2O + O2

here H2O2 is reduced to water and oxidised to O2

H2O2 + 2H+ + 2e- --> 2H2O reduction

H2O2 --> O2 + 2H+ + 2e- Oxidation

Another example:

Cl2 --> HCl + HOCl

Here the oxidation number of Cl goes from 0 to -1 in HCl, indicating a gain of electrons = reduction
And from 0 to +1 in HOCl, indicating a loss of electrons = oxidation