Which compound will show the highest reactivity towards electrophilic aromatic substitution: ${\text{C}}_6{\text{H}}_5{\text{OCH}}_3$, ${\text{C}}_6{\text{H}}_5{\text{CH}}_3$, ${\text{C}}_6{\text{H}}_5\text{Cl}$, or ${\text{C}}_6{\text{H}}_6$?

Solution

1. Reactivity towards electrophilic aromatic substitution increases with electron-donating groups.
2. The $-{\text{OCH}}_3$ group donates electrons via resonance (+M effect) more effectively than the $-{\text{CH}}_3$ group (hyperconjugation).
3. Chlorine is deactivating due to its strong inductive effect (-I) despite resonance (+M).
4. Benzene is the reference point with no substituents.
5. Hence the answer is (A).