What is formed when phenylacetylene reacts with dilute $HgSO_4$ in the presence of $H_2SO_4$?

$Ph-CH_2-CH=CH-CH_3$ $\xrightarrow[(ii) \text{ Alc. KOH}]{(i) \text{ } Br_2}$ ?

Give the industrial preparation method of ethyne.

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:

What is formed when acetylene reacts with alkaline $KMnO_4$?

$HC \equiv CNa + Cl - CH_2 - CH_2 - CH_2 - I \to (A)$; Major product $(A)$ is