Which of the following catalysts is used in the polymerization of $CH \equiv CH$ to $C_6H_6$?

The reagent$(s)$ for the following conversion is/are:
$Br-CH_2-CH_2-Br \xrightarrow{?} HC \equiv CH$

Carbon-carbon bond length is minimum in

Schemes $1$ and $2$ describe the sequential transformation of alkynes $M$ and $N$. Consider only the major products formed in each step for both the schemes.
$1.$ The product $X$ is:
$2.$ The correct statement with respect to product $Y$ is:
$(A)$ It gives a positive Tollens test and is a functional isomer of $X$.
$(B)$ It gives a positive Tollens test and is a geometrical isomer of $X$.
$(C)$ It gives a positive iodoform test and is a functional isomer of $X$.
$(D)$ It gives a positive iodoform test and is a geometrical isomer of $X$.

$1-$Butyne can be distinguished most easily from $2-$butyne by

What is the product when $2-$butyne is treated with liquid $NH_3$ in the presence of lithium?