Dilute aqueous solution of ........ acid is used as antibiotic. 

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 $\mathrm{AlCl}_5$

$H_3BO_3$ $\xrightarrow{{{T_1}}}X\xrightarrow{{{T_2}}}Y\xrightarrow{{red\,hot}}$ $B_2O_3$

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

If $B-Cl$ bond has a dipole moment, explain why $BCl_3$ molecule has zero dipole moment.

Alumina is

Explain the following :

$(1)$ Gallium has higher ionisation enthalpy than aluminum.

$(2)$ Boron does not exist as $B^{3+}$ ion.