When borax $\left( Na _{2} B _{4} O _{7}\right)$ is dissolved in water, it hydrolyses to form sodium hydroxide ( $NaOH$ ) and boric acid $\left( H _{3} BO _{3}\right)$ which can be written as $B ( OH )_{3}$ or $H _{3} BO _{3}$
$\underset{\text{(Borax)}}{Na _{2} B _{4} O _{7}}+7 H _{2} O \longrightarrow \underset{\text{(Sodium hydroxide)}}{2 NaOH} +\underset{\text{(Boric acid)}}{4 H _{3} BO _{3}}$