$Mg_2C_3 + H_2O \xrightarrow{X}$ (organic compound).
Compound $X$ is

Consider the following reaction sequences and choose the correct option:
$L \xrightarrow{Na/liq. NH_3} Ph-C \equiv C-Me \xrightarrow[Lindlar's \ Catalyst]{H_2, Pd/C} K$
$L \xrightarrow{HBr, \text{benzoyl peroxide}} N$
$K \xrightarrow{HBr} M$

Give the industrial preparation method of ethyne.

The reaction sequence is as follows:
$CH(COOK)=CH(COOK)_{(aq)}$ $\xrightarrow{\text{electrolysis}} X$ $\xrightarrow[Hg^{2+}]{dil. H_2SO_4} Y$; $Y$ is

$CH_3CH_2CH_2I$ $\xrightarrow{alc. KOH} A$ $\xrightarrow{Br_2} B$ $\xrightarrow{NaNH_2 / NH_3} C$. In this reaction,$C$ is:

When acetylene is passed through a solution of dilute sulfuric acid containing mercuric sulfate,the number of $\pi$ bonds in the final product obtained is.........