Boron halides behave as Lewis acids because of their

The structure of diborane $(B_2H_6)$ contains :-

$A$ certain salt $X$ gives the following results:
$(i)$ Its aqueous solution is alkaline to litmus.
$(ii)$ It swells up to a glassy material $Y$ on strong heating.
$(iii)$ When conc. $H_2SO_4$ is added to a hot solution of $X$,white crystals of an acid $Z$ separate out.
Identify $X, Y$ and $Z$ and write the equations for the reactions.

$A$ Lewis acid '$X$' reacts with $LiAlH_4$ in ether medium to give a highly toxic gas,'$Y$'. '$Y$' when heated with $NH_3$ gives a compound known as inorganic benzene. '$Y$' burns in oxygen and gives $H_2O$ and '$Z$'. '$Z$' is

The reason for boric acid being polymeric is .....

Which of the following orders is not correct against the given property?