What is the product formed by the hydration of propyne in the presence of $H_2SO_4$ and $HgSO_4$?

In the reaction $x + H_2O \xrightarrow[H_2SO_4]{HgSO_4} CH_3-CO-CH_2-CH_3$,the reactant $x$ is:

Identify the structure of the final product $(D)$ in the following sequence of reactions:
$Ph-CO-CH_3$ $\xrightarrow{PCl_5, \Delta} A$ $\xrightarrow{3 \text{ eq. } NaNH_2/NH_3} B$ $\xrightarrow{\text{Acidify}} C$ $\xrightarrow{1. B_2H_6, 2. H_2O_2/OH^-} D$
Total number of $sp^2$ hybridised carbon atoms in product $D$ is:

The general formula of an alkyne is:

The two carbon atoms in acetylene are

$CH \equiv CH$ $\xrightarrow{O_3/NaOH} X$ $\xrightarrow{Zn/CH_3COOH} Y$. '$Y$' is: