Which one of the following is correct statement

The number of neutrons present in the more abundant isotope of boron is ' $\mathrm{x}$ '. Amorphous boron upon heating with air forms a product, in which the oxidation state of boron is ' $y$ '. The value of $x+y$ is ...

Correct order of Lewis Acidic strength?

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 $\mathrm{AlCl}_5$

Give structure of gaseous $AlCl_3$. 

When borax is heated with $CoO$ on a platinum loop, blue coloured bead formed is largely due to