The composition of borax is:

$A$ nonmetallic element of group $13$,used in making bulletproof vests,is an extremely hard solid of black colour. It can exist in many allotropic forms and has an unusually high melting point. Its trifluoride acts as a Lewis acid towards ammonia. The element exhibits a maximum covalence of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why the trifluoride acts as a Lewis acid.

In group $13$ of the long form of the periodic table,an element $X$ has a boiling point of $T_2 \ (K)$ and a melting point of $T_1 \ (K)$. Identify the element $X$ for which $T_2 - T_1 \ (K)$ is maximum.

$Na_2B_4O_7 \stackrel{\text{heat}}{\longrightarrow} X + NaBO_2$
In the above reaction,the product $X$ is:

Maximum number of atoms which are present in one plane of $H_3BO_3$?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$2Na[Al(OH)_4] + CO_2 \longrightarrow 2Al(OH)_3 \downarrow + Na_2CO_3$