Which alkyne will give $3$-ethylhexane on catalytic hydrogenation?

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:

Which reacts with ammoniacal $AgNO_3$?

Which reagent is used for the following transformation? $Br-CH_2-CH_2-Br \rightarrow H-C \equiv C-H$

Which is the most acidic of the following?

Which of the following reagents is most suitable to distinguish compound $(3)$ from the others?
$(1) \ CH_3-C \equiv C-CH_3$
$(2) \ CH_3CH_2CH_2CH_3$
$(3) \ CH_3CH_2C \equiv CH$
$(4) \ CH_3CH=CH_2$