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

Identify the correct statement for $B _{2} H _{6}$ from those given below.

$(A)$ In $B _{2} H _{6}$, all $B - H$ bonds are equivalent.

$(B)$ In $B _{2} H _{6}$ there are four $3-$centre$-2-$electron bonds.

$(C)$ $B _{2} H _{6}$ is a Lewis acid.

$(D)$ $B _{2} H _{6}$ can be synthesized form both $BF _{3}$ and $NaBH _{4}$.

$(E)$ $B _{2} H _{6}$ is a planar molecule.

Choose the most appropriate answer from the options given below..... .

The structure of aluminium bromide is best represented as :

Alumina is insoluble in water because

Given below are two statements :

Statement $I$ : Boron is extremely hard indicating its high lattice energy

Statement $II$ : Boron has highest melting and boiling point compared to its other group members.

In the light of the above statements, choose the most appropriate answer from the options given below

Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out in the presence of