Disproportionation reaction, is a type of redox reaction involving simultaneous reduction and oxidation of atoms of the same element from one oxidation state (OS) to two different oxidation states.

$2\underset{-1}{{\mathrm{H}}_2{\mathrm{O}}_2}⟶2\underset{-2}{{\mathrm{H}}_2\mathrm{O}}+\underset{0}{{\mathrm{O}}_2^{}}$ : Disproportionation

$2{\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{HNO}}_3+{\mathrm{HNO}}_2$ : Disproportionation

${\mathrm{MnO}}_4^{-}+4{\mathrm{H}}^{+}+3{\mathrm{e}}^{-}\to {\mathrm{MnO}}_2+2{\mathrm{H}}_2\mathrm{O}$ : reduction only

$3{\mathrm{MnO}}_4^{2-}+4{\mathrm{H}}^{+}\to 2{\mathrm{MnO}}_4^{-}+{\mathrm{MnO}}_2^{+4}+2{\mathrm{H}}_2\mathrm{O}$ : Disproportionation