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

Observe the following reactions (not balanced):
$BF_3 + LiAlH_4 \xrightarrow{(C_2H_5)_2O} X + LiF + AlF_3$
$X + NaH \longrightarrow Y$
The incorrect statement about $Y$ is:

Which of the following shows dimerisation?

When $AlCl_3 \cdot 6H_2O$ is strongly heated,then it forms

In the following reaction,assign the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{B}_2O_3 + 3H_2O \longrightarrow 2H_3BO_3$

The number of three-centre two-electron $(3c-2e)$ bonds in a molecule of diborane $(B_2H_6)$ is