Boric acid,$H_3BO_3$,is a/an ....

Given below are two statements:
Statement $I$: Aluminium is more electropositive than thallium as the standard electrode potential value of $E^\circ_{Al^{3+}/Al}$ is negative and $E^\circ_{Tl^{3+}/Tl}$ is positive.
Statement $II$: The sum of first three ionization enthalpies of boron is very high when compared to that of aluminium. Due to this reason, boron forms covalent compounds only and aluminium forms $Al^{3+}$ ion.

Diborane reacts with ammonia under different conditions to give a variety of products. Which one among the following is not formed in these reactions?

The reason for the polymeric nature of boric acid is .....

Anhydrous $AlCl_3$ is obtained from

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.