Which of the following metal carbides gives propyne on hydrolysis?

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

The number of possible structural alkynes with molecular formula $C_5H_8$ is

In the given reaction $x$ is:
$CH_3 - C \equiv CH$ $\xrightarrow{Excess\ HCl} (A)$ $\xrightarrow{H_2O/OH^{-}} (x)$

An alkyne has the molecular formula $C_6H_{10}$. The number of $1$-alkyne isomers (excluding stereoisomers) possible for it is

Which one of the following carbonyl compounds cannot be prepared by addition of water on an alkyne in the presence of $HgSO_4$ and $H_2SO_4$?