Among the following, the correct statement(s) is(are)

$[A]$ $\mathrm{A} 1\left(\mathrm{CH}_3\right)_3$ has the three-centre two-electron bonds in its dimeric structure

$[B]$ $\mathrm{BH}_3$ has the three-centre two-electron bonds in its dimeric structure

$[\mathrm{C}] \mathrm{AlCl}_3$ has the three-centre two-electron bonds in its dimeric structure

$[D]$ The Lewis acidity of $\mathrm{BCl}_5$ is greater than that of $\mathrm{AlCl}_5$

In some of the reactions thallium resembles aluminium, whereas in others it resembles with group $-I$ metals. Support this statement by giving some evidences. 

A neutral molecule $XF_3$ has a zero dipole moment. The element $X$ is most likely

In $B_2H_6$

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 :

The correct order of atomic radii in group $13$ elements is