When hydrogen peroxide is added to acidified solution of dichromate...

When $\mathrm{H}_2 \mathrm{O}_2$ is added to an acidified solution of dichromate $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$, a deep blue complex chromic peroxide, $\mathrm{CrO}_5$ is formed. $\mathrm{Cr}_2 \mathrm{O}_7^{2-}+2 \mathrm{H}^{+}+4 \mathrm{H}_2 \mathrm{O}_2 \longrightarrow 2 \mathrm{CrO}\left(\mathrm{O}_2\right)_2+5 \mathrm{H}_2 \mathrm{O}$ This deep blue coloured complex has the following structure Let the oxidation state of Cr be x . In $\mathrm{CrO}\left(\mathrm{O}_2\right)_2$$\begin{aligned} x+(-1) 4+(-2) & =0 \\ x-6 & =0 \\ x & =+6\end{aligned}$$$