What is $Z$ in the following reactions?
$BCl_3 + H_2 \xrightarrow[450^{\circ}C]{Cu-Al} X + HCl$
$X \xrightarrow{\text{methylation}} Z$

Diborane on hydrolysis gives a compound $X$. The correct statements about $X$ are
$I$. It is a tribasic acid
$II$. It is a weak monobasic acid
$III$. It has a layer structure
$IV$. It is highly soluble in water

In the given structure of Diborane,$\theta_1$ and $\theta_2$ are respectively:

$STATEMENT-1$: In water,orthoboric acid behaves as a weak monobasic acid. because
$STATEMENT-2$: In water,orthoboric acid acts as a proton donor.

Give the increasing order of group $13$ elements for atomic radius.

$A$ black coloured element with $ns^2 np^1$ outer electronic configuration cannot react with air in its crystalline form. However,in amorphous form,it gives an oxide in air which is acidic in nature. Identify the element.