a
\(M(OH)_2  ⇌ [M^{+2}]  [OH^{-1}]^2\)

                    \( (s)\)   \( (2s)^2\)

\(K_{sp} = 4s^3\)          \(4s^3 = 32 \times 10^{-12} \)     

\({s^3} = \frac{{32 \times {{10}^{ - 12}}}}{4} = 8 \times {10^{ - 12}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,s = {(8 \times {10^{ - 12}})^{1/3}} = 2.0 \times {10^{ - 4}}\)

\([O{H^ - }] = 2 \times 2.0 \times {10^{ - 4}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,[O{H^ - }] = 4.0 \times {10^{ - 4}}\,\,pOH = 4 - \log 4\)