What is a disproportionation reaction? Give an example.

(N/A) disproportionation reaction is a special type of redox reaction in which the same element in a single species is simultaneously oxidized and reduced.
Example: The reaction of white phosphorus $(P_4)$ with sodium hydroxide $(NaOH)$ to form phosphine $(PH_3)$ and sodium hypophosphite $(NaH_2PO_2)$.
$P_4 + 3NaOH + 3H_2O \rightarrow PH_3 + 3NaH_2PO_2$
In this reaction,the oxidation state of phosphorus changes from $0$ in $P_4$ to $-3$ in $PH_3$ (reduction) and to $+1$ in $NaH_2PO_2$ (oxidation).