Hydrogenation of $2-$Butyne in the presence of Lindlar's catalyst gives

Write structures of different isomers corresponding to the $5^{th}$ member of alkyne series. Also write $IUPAC$ names of all the isomers. What type of isomerism is exhibited by different pairs of isomers?

$HC\equiv CH + 2HOCl \rightarrow A$. What is the product $A$?

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

In the reaction,$CH_3-C \equiv C-CH_3 \xrightarrow{(i) X, (ii) Zn/H_2O} CH_3-C(=O)-C(=O)-CH_3$,$X$ is:

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 $Y$.