Chemistry - Ionic Equilibrium Question with Solution | TestHub

Condition for precipitation ${\mathrm{Q}}_{\text{ip }}>{\mathrm{K}}_{\text{sp }}$
For $\left[\mathrm{A}(\mathrm{OH}{)}_2\right]$
$\begin{array}{rl}& \left[{\mathrm{A}}^{2+}\right][\mathrm{OH}{]}^2>9\times 10^{-10}\\ & \left[{\mathrm{A}}^{+2}\right]=1\mathrm{M}\\ & \Rightarrow \left[{\mathrm{OH}}^{-}\right]>3\times 10^{-5}\mathrm{M}\end{array}$

For $\left[\mathrm{B}(\mathrm{OH}{)}_3\right]$
$\begin{array}{rl}& \left[{\mathrm{B}}^{3+}\right]{\left[{\mathrm{OH}}^{-}\right]}^3>27\times 10^{-18}\\ & \left[{\mathrm{B}}^{3+}\right]=1\mathrm{M}\\ & \Rightarrow \left[{\mathrm{OH}}^{-}\right]>3\times 10^{-6}\mathrm{M}\end{array}$

So, $\mathrm{B}(\mathrm{OH}{)}_3$ will precipitate before $\mathrm{A}(\mathrm{OH}{)}_2$