$\mathrm{Cr}{\left(\mathrm{OH}\right)}_3+{\mathrm{H}}_2{{\mathrm{O}}_2}^{\stackrel{\text{ Alkali }}{\to }}{\mathrm{CrO}}_4^{2-}+{\mathrm{H}}_2\mathrm{O}$   The number of   $O{H}^{-}$ required to balance the above equation _____

$$\begin{gathered} \stackrel{+3}{\mathrm{Cr}}{\left(\mathrm{OH}\right)}_3+{\mathrm{H}}_2{\stackrel{-1}{\mathrm{O}}}_2\stackrel{\mathrm{Alkali}}{\to } \stackrel{+6}{\mathrm{Cr}}{O}_4^{2-}+{\mathrm{H}}_2\stackrel{-2}{\mathrm{O}} \\ \mathrm{According} \mathrm{to} \mathrm{oxidation} \mathrm{no}. \mathrm{method} \\ 2\mathrm{Cr}{\left(\mathrm{OH}\right)}_3+3{\mathrm{H}}_2{\mathrm{O}}_2\to 2{\mathrm{CrO}}_4^{-2}+{\mathrm{H}}_2\mathrm{O} \\ 2\mathrm{Cr}{\left(\mathrm{OH}\right)}_3+3{\mathrm{H}}_2{\mathrm{O}}_2+4{\mathrm{OH}}^{-}\to 2{\mathrm{CrO}}_4^{-2}+8{\mathrm{H}}_2\mathrm{O} \end{gathered}$$