Which among the following is the strongest acid?

The number of chlorine atoms present in the organic products $X$ and $Y$ of the following reactions,respectively,are:
$\text{Benzene} + 6Cl_2 \xrightarrow[\text{dark, cold}]{\text{Anhydr. } AlCl_3} X$
$\text{Benzene} + 3Cl_2 \xrightarrow{UV, 500 \text{ K}} Y$

Complete the following reactions and identify $A, B, C$ respectively:
$(i)$ $\text{Phenol} + A \xrightarrow{\text{distill}} \text{Benzene}$
(ii) $\text{Benzenesulfonic acid} + B \xrightarrow{150-200^{\circ}C, \text{HCl, high pressure}} \text{Benzene}$
(iii) $\text{Chlorobenzene} \xrightarrow{C, \text{NaOH}} \text{Benzene}$

Conversion of hexane into benzene involves the reaction of:

The nitro group in nitrobenzene is a

Among the following,the set which represents aromatic species is: