The most reactive compound among the following for electrophilic aromatic substitution is:

Electrophilic aromatic substitution is faster in benzene rings that have electron-donating groups (activating groups) attached to them. These groups increase the electron density in the ring, particularly at the ortho and para positions, making it more susceptible to electrophilic attack.

1. Activating Groups: Groups like -OH, -NH₂, -OCH₃, and -CH₃ activate the ring. The -OH group in phenol is strongly activating due to the resonance (+R) effect of the lone pair on the oxygen atom .
2. Deactivating Groups: Groups like -NO₂, -CN, and -COOH withdraw electrons (via -I and -R effects), deactivating the ring . Halogens (-Cl, -Br) are also deactivating due to the strong -I effect, although they are ortho-para directing .
3. Conclusion: Although the specific structures for the options are missing in the input, based on the subtopic 'Phenols', the correct answer (Option 4) is likely Phenol (or a similar highly activated compound like Aniline), which is significantly more reactive than benzene or halosubstituted benzenes towards electrophilic substitution.