Which of the following is used for the conversion of $2$-hexyne into $trans$-$2$-hexene?

The major product of the following reaction is $P$. Number of oxygen atoms present in product $P$ is $. . . . . . . . . . . (nearest integer)$.

The end product of the following sequence is
$CaC_2$ $\xrightarrow{H_2O} B$ $\xrightarrow[HgSO_4]{H_2O, H_2SO_4} C$

Identify product $B$ in the following sequence of reactions.
$1,2-\text{Dibromoethane}$ $\xrightarrow[\text{alc. } KOH]{\Delta} A$ $\xrightarrow{NaNH_2} B$

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

The catalyst used in the dimerization of acetylene to prepare chloroprene is: