Number of bridged  $\mathrm{B}-\mathrm{O}-\mathrm{B}$and terminal  $\mathrm{B}-\mathrm{OH}$ bonds present in tetraborate ion are respectively

Tetraborate ion is a tetranuclear complex. It has 5 bridged $\mathrm{B}-\mathrm{O}-\mathrm{B}$bonds and 4 $\mathrm{terminal} \mathrm{B}-\mathrm{OH}$ bonds.

Two Boron atoms involve in ${\mathrm{sp}}^2$ hybridization and remaining two Boron atoms invove in${\mathrm{sp}}^3$ hybridization.