The number of $P-H$ bond$(s)$ in $H_3PO_2, H_3PO_3$ and $H_3PO_4$,respectively,is

The weakest Lewis acid is

Write balanced equations for :
$(i) \, BF_{3} + LiH \to $
$(ii) \, B_{2}H_{6} + H_{2}O \to $
$(iii) \, NaH + B_{2}H_{6} \to $
$(iv) \, H_{3}BO_{3} \xrightarrow{\Delta }$
$(v) \, Al + NaOH \to $
$(vi) \, B_{2}H_{6} + NH_{3} \to $

When orthoboric acid $(H_3BO_3)$ is subjected to strong heating, the residue left 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. $H_2SO_4$ 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.

Aluminium chloride exists as a dimer,$Al_2Cl_6$,in the solid state as well as in solutions of non-polar solvents such as benzene. When dissolved in water,it gives: