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

Aluminium $(III)$ chloride forms a dimer because ........

In diborane $(B_2H_6)$, the number of electrons that accounts for bonding in the bridges is

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{B}F_3 + 3H_2O \longrightarrow H_3BO_3 + 3HF$

Identify the correct statement for $B_2H_6$ from those given below.
$(A)$ In $B_2H_6$,all $B-H$ bonds are equivalent.
$(B)$ In $B_2H_6$ there are four $3$-centre-$2$-electron bonds.
$(C)$ $B_2H_6$ is a Lewis acid.
$(D)$ $B_2H_6$ can be synthesized from both $BF_3$ and $NaBH_4$.
$(E)$ $B_2H_6$ is a planar molecule.
Choose the most appropriate answer from the options given below.

The correct statements from the following are:
$(A)$ The decreasing order of atomic radii of group $13$ elements is $Tl > In > Ga > Al > B$.
$(B)$ Down the group $13$ electronegativity decreases from top to bottom.
$(C)$ $Al$ dissolves in dil. $HCl$ and liberates $H_2$,but conc. $HNO_3$ renders $Al$ passive by forming a protective oxide layer on the surface.
$(D)$ All elements of group $13$ exhibit a highly stable $+1$ oxidation state.
$(E)$ Hybridisation of $Al$ in $[Al(H_2O)_6]^{3+}$ ion is $sp^3d^2$.
Choose the correct answer from the options given below: