$2$-Hexyne reacts with $.......$ to give $trans-2$-hexene.

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

$Alkyne \xrightarrow[{Hg^{2+}}]{{H^+/H_2O}} \text{ketone}$
Which of the following alkynes cannot give a ketone?

$2CaC_2$ $\xrightarrow{H_2O} X$ $\xrightarrow{Cu_2Cl_2 + NH_4Cl} Y$ ; $Y$ is

$H_3C-C \equiv CH$ $\xrightarrow{NaNH_2} A$ $\xrightarrow{CH_3CH_2Br} B$ $\xrightarrow{H_2/Pd, BaSO_4} C$
Identify product $(C)$?

Which of the following would be produced when acetylene reacts with $HCl$?