Cr(OH)₃ + H₂O₂$\stackrel{\mathrm{Alkali}}{\to }$CrO₄^-2 + H₂O. The number of OH^– required to balance the above equation

$$\begin{gathered} \stackrel{+3}{\mathrm{Cr}}{\left(\mathrm{OH}\right)}_3+ {\mathrm{H}}_2\stackrel{-1}{{\mathrm{O}}_2} \stackrel{ \mathrm{Alkali} }{\to } \stackrel{+6}{\mathrm{Cr}}{\mathrm{O}}_4^{-2}+ {\mathrm{H}}_2\stackrel{-2}{\mathrm{O}}. \\ \mathrm{Cross} \mathrm{multiply} \mathrm{the} \mathrm{oxidation} \mathrm{states} \mathrm{and} \mathrm{then} \mathrm{balence} \mathrm{it} \\ 2\mathrm{Cr}{\left(\mathrm{OH}\right)}_3+3 {\mathrm{H}}_2{\mathrm{O}}_2+4{\mathrm{OH}}^{-} \to 2 {\mathrm{CrO}}_4^{-2}+ 4{\mathrm{H}}_2\mathrm{O}+4{\mathrm{H}}_2\mathrm{O} \end{gathered}$$