Which series of reagents can be used to convert acetylene into higher alkynes?

Which reactants are used to prepare $cis$ and $trans$ alkenes from alkynes?

An unknown compound $X$ is an unsaturated hydrocarbon. It reacts with $HgSO_4$ and $H_2SO_4$ to give compound $(B)$. Compound $(B)$ on oxidation gives compound $(C)$. Compound $(C)$ on reaction with $NaOH$ and soda lime gives methane. Identify $A$ (which is $X$),$B$,and $C$ by providing the chemical reactions.

When acetylene is passed into dilute sulphuric acid containing $Hg^{2+}$ ions,the product formed is

Predict the product $C$ obtained in the following reaction of $1-$butyne: $CH_3-CH_2-C \equiv CH + HCl$ $\rightarrow B$ $\xrightarrow{HI} C$

$CH_{3}C \equiv CMgBr$ can be prepared by the reaction of: