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

Select the correct statements from the following:
$A$) Aluminium liberates $H_2$ gas with dil. $HCl$ but not with aqueous $NaOH$.
$B$) Formula of sodium metaborate is $Na_3BO_3$.
$C$) Boric acid is a weak monobasic acid.
$D$) For thallium,$+1$ state is more stable than $+3$ state.

The element which has the least metallic character is ..........

Given below are two statements :
Statement $I$ : Gallium is used in the manufacturing of thermometers.
Statement $II$ : $A$ thermometer containing gallium is useful for measuring the freezing point $(256 \ K)$ of brine solution.
In the light of the above statement,choose the correct answer from the options given below :

$Al_2O_3$ reacts with

Boron trifluoride on reaction with lithium aluminium hydride in ether gives $LiF$, $AlF_3$ and $X$. $X$ on reaction with $NH_3$ gives $Y$. $Y$ on further heating gives a compound $Z$. The number of $\sigma$-bonds and $\pi$-bonds in $Z$ are $x$ and $y$ respectively. $(x+y)$ is equal to