Give industrial preparation for diborane. 

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$:

Assertion $A$ : The stability order of +$1$ oxidation state of $\mathrm{Ga}$, In and $\mathrm{Tl}$ is $\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}$.

Reason $R$ : The inert pair effect stabilizes the lower oxidation state down the group.

In the light of the above statements, choose the correct answer from the options given below :

Describe the shapes of $BF $$_{3}$ and $BH _{4}^{-}$. Assign the hybridisation of boron in these species.

The incorrect statement from the following for borazine is:

$(i)\,Al\,\xrightarrow{{{N_2}}}\,A$         $(ii)\,Al\,\xrightarrow{c}\,B$

Here $A$ and $B$ on hydrolysis respectively gives

$BCl_3$, exists as monomer whereas $AlCl_3$ is dimerized through halogen bridging. Give reason. Explain the structure of the dimer of $AlCl_3$ also.