How many isomers are possible for pentyne $(C_5H_8)$?

$A$ $\xrightarrow[1\% \ HgSO_4]{20\% \ H_2SO_4} B$ $\xrightarrow{I_2 + NaOH} C + C_6H_5COONa$. The reactant $A$ is

$Be_2C + H_2O \rightarrow Be(OH)_2 + X$
$CaC_2 + H_2O \rightarrow Ca(OH)_2 + Y$
Then $X$ and $Y$ are respectively:

Which is the most suitable reagent among the following to distinguish compound $(3)$ from the others?
$(1) \ CH_3-C \equiv C-CH_3$
$(2) \ CH_3-CH_2-CH_2-CH_3$
$(3) \ CH_3-CH_2-C \equiv CH$
$(4) \ CH_3-CH=CH_2$

What is obtained by the reaction of calcium carbide with heavy water?

Identify the structure of $M$ based on the following reaction scheme: