$N{a_2}{B_4}{O_7}.10{H_2}O \xrightarrow{\Delta } X + NaB{O_2} + {H_2}O$

$X + C{r_2}{O_3}\xrightarrow{\Delta }Y$ (Green coloured)

$X$ and $Y$ are

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 $\mathrm{AlCl}_5$

Identify the compounds $A, X$ and $Z$ in the following reactions : 

$A + 2HCl + 5{H_2}O \to 2NaCl + X$

$X\xrightarrow[{370\,K}]{\Delta }HB{O_2}\xrightarrow[{ > 370\,K}]{\Delta }Z$

Which reaction involves a change in the electron pair geometry for the underlined element ?

$STATEMENT$-$1$: In water, orthoboric acid behaves as a weak monobasic acid. because

$STATEMENT$-$2$: In water, orthoboric acid acts as a proton donor.

Which of the following is correct ?