Friedel Crafts alkylation of chlorobenzene is an example of

The correct answer is Option (4) → electrophilic substitution

The benzene ring is rich in π electrons, so its typical reactions are electrophilic substitution: an electron-poor species (E⁺) attacks the ring and replaces a hydrogen atom, and the aromatic ring is kept. Haloarenes also react this way, with the new group going to the ortho and para positions.

In Friedel–Crafts alkylation, anhydrous \( \ce{AlCl3} \) pulls the chlorine away from the alkyl halide and produces the electrophile, the methyl carbocation:

    \( \displaystyle \ce{CH3Cl + AlCl3 -> CH3^+ + AlCl4^-} \)

The \( \ce{CH3^{+}} \) then attacks chlorobenzene at the ortho and para positions:

    \( \displaystyle \ce{C6H5Cl + CH3Cl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{CH3C6H4Cl + HCl} \)

The products are 2-chlorotoluene (minor) and 4-chlorotoluene (major). Friedel–Crafts acylation of chlorobenzene works in the same way, with \( \ce{CH3CO^{+}} \) as the electrophile:

    \( \displaystyle \ce{C6H5Cl + CH3COCl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{CH3COC6H4Cl + HCl} \)

Both are examples of electrophilic substitution.

Why the other options are incorrect

• Option (1) nucleophilic substitution — Incorrect. Here a nucleophile would replace the chlorine atom. Haloarenes resist this because the C–Cl bond has partial double bond character; it happens only under drastic conditions (NaOH at 623 K and 300 atm gives phenol).

• Option (2) free radical substitution — Incorrect. This is the path of halogenation of alkanes or of the side chain of toluene in sunlight, not of a reaction catalysed by \( \ce{AlCl3} \).

• Option (3) nucleophilic addition — Incorrect. This is the typical reaction of the C=O group of aldehydes and ketones. The aromatic ring does not add reagents, as that would destroy its stability.

NCERT (2026-27 edition):
Electrophilic Substitution Reactions

Note: The same/similar question has been asked in different years by NTA as per the details given below: