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 $\mathrm{AlCl}_5$

Given below are two statements:

Statement $I$ : The decrease in first ionization enthalpy from $B$ to $Al$ is much larger than that from $Al$ to $Ga$.

Statement $II$ : The d orbitals in Ga are completely filled.

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

The stability of $+ 1$ oxidation state among $Al,Ga, In$ and $Tl$ increases in the sequence

${H_3}B{O_3}\,\xrightarrow{{{T_1}}}X\,\xrightarrow{{{T_2}}}Y\,\xrightarrow{{\operatorname{Re} d\,\,\,hot}}{B_2}{O_3}$

if $T_1 < T_2$ then $X$ and $Y$ respectively are

When $Al$ is added to $KOH$ solution

Alumina is insoluble in water because