Which of the following compound is formed in borax bead test?

In the metallurgy of aluminium, cryolite is mixed in the molten state because it

Select the incorrect statement

$(a)$ $PCl_5$ form weak monobasic acid during hydrolysis
$(b)$ In $B_3N_3H_6$ nucleophile attack on $B-$ atom
$(c)$ $Al_2Cl_6$ is a polar and planar molecule
$(d)$ In $AlF_3$, hybridisation of $Al$ is $sp^2$

Why does boron trifluoride behave as a Lewis acid ?

The structure of aluminium bromide is best represented as :

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 crystal of an acid $Z$ separates out.

Write equations for all the above reactions and identify $X, Y$ and $ Z$.