JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Redox Reactions and Electrochemistry

In a disproportionation the same element is both oxidised and reduced in one reaction. In $2\mathrm{CuBr}\to \mathrm{CuBr}{}_2+\mathrm{Cu}$, copper begins in the $+1$ state and ends partly as $\mathrm{Cu}{}^{2+}$ in $\mathrm{CuBr}{}_2$ (oxidised) and partly as metallic $\mathrm{Cu}$ with oxidation state $0$ (reduced). This splitting of one oxidation state into a higher and a lower one is the hallmark of disproportionation.