The correct statement$(s)$ for orthoboric acid is/are

$(A)$ It behaves as a weak acid in water due to self ionization.

$(B)$ Acidity of its aqueous solution increases upon addition of ethylene glycol.

$(C)$ It has a three dimensional structure due to hydrogen bonding.

$(D)$ It is weak electrolyte in water.

Aluminium trifluoride is insoluble in anhydrous $HF$ but dissolves on addition of $NaF$. Aluminium trifluoride precipitates out of the resulting solution when gaseous $BF_3$, is bubbled through. Give reasons.

During the borax bead test with $CuSO _4$, a blue green colour of the bead was observed in oxidising flame due to the formation of

The function of fluorspar in the electrolytic reduction of alumina dissolved in fused cryolite $(Na_3AlF_6)$ is :

Outermost electronic configuration of a group $13$ element, $E$, is $4 \,\mathrm{~s}^{2}, 4 p^{1}$. The electronic configuration of an element of $p$-block period-five placed diagonally to element, $E$ is :

When orthoboric acid $({H_3}B{O_3})$ is heated, the residue left is