Condition for precipitation Qip >Ksp For [A(OH)2] $\begin{aligned}
& {\left[\mathrm{A}^{2+}\right][\mathrm{OH}]^2>9 \times 10^{-10}} \
& {\left[\mathrm{A}^{+2}\right]=1 \mathrm{M}} \
& \Rightarrow\left[\mathrm{OH}^{-}\right]>3 \times 10^{-5} \mathrm{M}
\end{aligned}For\left[\mathrm{B}(\mathrm{OH})_3\right]\begin{aligned}
& {\left[\mathrm{B}^{3+}\right]\left[\mathrm{OH}^{-}\right]^3>27 \times 10^{-18}} \
& {\left[\mathrm{B}^{3+}\right]=1 \mathrm{M}} \
& \Rightarrow\left[\mathrm{OH}^{-}\right]>3 \times 10^{-6} \mathrm{M}
\end{aligned}So,\mathrm{B}(\mathrm{OH})_3willprecipitatebefore\mathrm{A}(\mathrm{OH})_2$