$H_3BO_3$ is

Match Column-$I$ with Column-$II$ :

Column-$I$	Column-$II$
$A$. $Bi^{+3} \to (BiO)^{+}$	$P$. Heat
$B$. $[AlO_2]^{-} \to Al(OH)_3$	$Q$. Hydrolysis
$C$. $SiO_4^{-4} \to Si_2O_7^{-6}$	$R$. Acidification
$D$. $(B_4O_7)^{-2} \to [B(OH)_3]$	$S$. Dilution with water

What is the decreasing order of Lewis acid strength of boron halides?

When orthoboric acid $(H_3BO_3)$ is heated,the residue left is:

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:

When orthoboric acid is heated,the residue left is ...