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

The structure of the product $(Z)$ in the reactions given below is:
$HC \equiv CH$ $\xrightarrow{NaNH_2, CH_3COCH_3, H^{+}} X$ $\xrightarrow{Hg^{2+}, H_3O^{+}, H_2O} Z$

Which of the following has the shortest $C - C$ bond length?

The final product obtained by heating ethyne in the presence of $HgSO_4$ and dilute $H_2SO_4$ at $333 \ K$ is .........

To convert $1$-butyne to $1-D$-butanal,one would carry out the following steps :
$(I)$ Sodium amide,then $D_2O$
$(II)$ Disiamylborane,then hydrogen peroxide/sodium hydroxide
$(III)$ The transformation can not be carried out with the indicated reagents.

In which of the following cases is the bond length between carbon and nitrogen minimum?