Which is the most reactive hydrocarbon among the following?

Maximum bond energy of $C-H$ bonds is found in the compound:

Identify the major product of the following reaction:

The reaction of $2-$pentyne with dilute $H_2SO_4$ and $HgSO_4$ yields...............

In the reaction
$HC \equiv CH \xrightarrow[(ii) CH_3CH_2Br]{(i) NaNH_2 / liq. NH_3} X$
$\xrightarrow[(ii) CH_3CH_2Br]{(i) NaNH_2 / liq. NH_3} Y$
$X$ and $Y$ are

When acetylene reacts with $HCl$ in the presence of $HgCl_2$,the product is