In alkaline medium, ${\mathrm{H}}_2{\mathrm{O}}_2$ reacts with ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ respectively to give

$$\begin{gathered} 2\mathrm{Fe}{\left[{\left(\mathrm{CN}\right)}_6\right]}_{\left(\mathrm{s}\right)}^{3-} + {\mathrm{H}}_2{\mathrm{O}}_{2\left(\mathrm{l}\right)} + 2{\mathrm{OH}}_{\left(\mathrm{aq}\right)}^{-} \to \\ 2\mathrm{Fe}{\left[{\left(\mathrm{CN}\right)}_6\right]}_{\left(\mathrm{s}\right)}^{4-} + 2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)} + {\mathrm{O}}_{2\left(\mathrm{l}\right)} \left({\mathrm{Fe}}^{3+} \to {\mathrm{Fe}}^{2+}\right) \\ \mathrm{and} {\mathrm{Mn}}^{2+} + {\mathrm{H}}_2{\mathrm{O}}_2 \to {\mathrm{Mn}}^{4+} + 2{\mathrm{OH}}_{ }^{-} (\mathrm{Mn}+2 \mathrm{to} \mathrm{Mn}+4) \end{gathered}$$