${\mathrm{k}}_{\mathrm{sp}}$ of a saturated solution of $\text{B}{\text{(OH)}}_2$ of ${\text{p}}^{\text{H}}$10 is 

$\text{B}{\left(OH\right)}_2\stackrel{ }{\rightleftharpoons }\underset{s}{\overset{2+}{B}}+2\underset{2s}{\overset{-}{OH}}$

${\mathrm{p}}^H=10\therefore {\mathrm{p}}^{\mathrm{OH}}=4\therefore \overline{\mathrm{O}}\mathrm{H}={10}^{-4}=2\mathrm{s}$

$\therefore s=\frac{{10}^{-4}}{2}=5\times {10}^{-5}$

$\therefore k_{sp}=\left(5\times {10}^{-5}\right){\left({10}^{-4}\right)}^2$

$=5\times {10}^{-5}\times {10}^{-8}$

$=5\times {10}^{-13}{M}^3$