The electrolysis of aqueous potassium maleate gives which of the following products?

When $Mg_2C_3$ is reacted with water,a compound $X$ is formed which on heating with $Na$ followed by treatment with $C_2H_5Br$ gives another compound $Y$. Calculate the number of sigma bonds in $Y$.

$C_2H_2$ $\xrightarrow[1\% HgSO_4]{dil. H_2SO_4} A$ $\xrightarrow{[O]} B$ $\xrightarrow{NaOH} C$ $\xrightarrow{NaOH/CaO} D$,$[D]$ is:

Acetylene reacts with a $42\% H_2SO_4$ solution containing $1\% HgSO_4$ to give

$CH_3-C \equiv C-O-CH_3 \xrightarrow{dil. H_2SO_4, HgSO_4} \text{major product}$

Propyne on cyclic polymerisation gives