Which one of the following elements is unable to form $MF_{6}^{3-}$ ion?

Which of the following is not correct regarding Orthoboric acid $(H_3BO_3)$?

Boron halides behave as Lewis acids because of their nature.

The correct statement is:

$A$ 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. $H_{2}SO_{4}$ is added to a hot solution of $X,$ white crystals of an acid $Z$ separate out.
Write equations for all the above reactions and identify $X, Y,$ and $Z$.

The number of water molecules present in borax,kernite and bauxite respectively are