Which reactant is used to prepare trans alkene from alkyne?

When acetylene reacts with $HCl$ in the presence of $HgCl_2$,the product formed is.........

$A$ salt-producing hydrocarbon among these compounds is

Compound $(X)$ [styrene] is subjected to the following sequence of reactions: $(i)$ $Br_2/CHCl_3$,$(ii)$ $NaNH_2$ (excess),$(iii)$ $CH_3I$,$(iv)$ $H_2, Na/NH_3(l)$,giving Major Product $(Y)$. The molar mass of the major product $(Y)$ formed is . . . . . . $\text{g mol}^{-1}$. (Given molar mass in $\text{g mol}^{-1}$: $C:12, H:1$)

What is Lindlar's catalyst? Write its uses.

What type of bonds are formed between two carbon atoms in acetylene?