Which one of the following molecular hydrides acts as a Lewis acid?

In the following reactions:
$3B_2H_6 + 6NH_3 \text{ (excess)} \xrightarrow{\Delta} 2B_3N_3H_6 + 12H_2$
$6NaH + 2BF_3 \xrightarrow{450 \ K} B_2H_6 + 6NaF$
$B_2H_6 + 6H_2O \longrightarrow 2H_3BO_3 + 6H_2$
$X, Y$ and $Z$ are respectively:

Which pair of oxides is acidic in nature?

Explain the physical and chemical properties of borax.

What is the molecular formula of borazole?

Identify the correct statements from the following:
$(i)$ The atomic radius of $Al$ is lower than the atomic radius of $Ga$.
$(ii)$ Boron exists in many allotropic forms.
$(iii)$ The melting point of $Ga$ is lowest among the group $13$ elements.