The electrophile used in the sulfonation of benzene is..........

The following compound has four aromatic rings marked as $A$,$B$,$C$ and $D$. Rank them in terms of increasing reactivity towards electrophilic aromatic substitution?

Among the given organic compounds,the total number of aromatic compounds is $....$.

Among the following compounds $(I-III)$,the correct order of reactivity towards electrophilic substitution reaction is:

Which of the following compounds is most reactive to an aqueous solution of sodium carbonate $?$ (The structures correspond to cyclic hydrocarbons with varying degrees of unsaturation).

The correct order of reactivity towards Electrophilic Substitution Reaction $(E.S.R.)$ for the following compounds is:
$(i)$ Toluene
(ii) $m$-Methoxytoluene
(iii) Benzaldehyde
(iv) $p$-Nitrobenzaldehyde