The empirical formula of the compound ' $D$ ' formed in the given reaction sequence is

$$ \mathrm{C}_2 \mathrm{H}_4 \xrightarrow{\mathrm{Br}_2 / \mathrm{CCl}_4} A \xrightarrow[\text { (ii) } \mathrm{NaNH}_2]{\text { (i) } \mathrm{Alc} \cdot \mathrm{KOH}} B \xrightarrow[\text { polymerisation }]{\text { Cyclic }} C \xrightarrow[\text { DryAlCla }{ }_3 \text {, dark.cold }]{\mathrm{Cl}_2 \text { (excess) }} $$

What is the product ' $Z$ ' in the following reaction sequence?

$$ \mathrm{C}_6 \mathrm{H}_5 \mathrm{~N}_2 \mathrm{Cl} \xrightarrow[\mathrm{HCl}]{\mathrm{Cu}_2 \mathrm{Cl}_2} X \xrightarrow[\text { Na/dry ether }]{\mathrm{CH}_3 \mathrm{Cl}} Y \xrightarrow[\text { Dark }]{\mathrm{Cl}_2 / \mathrm{Fe}} Z $$

Which of the following is the most reactive towards $\mathrm{S}_{\mathrm{N}} 1$ mechanism?