Friedel-Craft reaction as shown below is an example of

The correct answer is Option (1) → Electrophilic substitution reaction

In a Friedel-Crafts alkylation, anhydrous \( \ce{AlCl3} \), a Lewis acid, pulls the chlorine away from the alkyl halide and produces an electrophile, here the methyl cation from methyl chloride:

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

The electrophile attacks the benzene ring of chlorobenzene and a hydrogen of the ring is lost as \( \ce{H+} \), which regenerates the catalyst (\( \ce{H+ + AlCl4^- -> HCl + AlCl3} \)). A ring hydrogen is replaced by the methyl group and the aromatic ring is kept, so this is electrophilic substitution:

    \( \displaystyle \ce{C6H5Cl + CH3Cl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \text{1-chloro-2-methylbenzene (minor)} + \text{1-chloro-4-methylbenzene (major)} + \ce{HCl} \)

Chlorine deactivates the ring slightly, but its lone pairs direct the electrophile to the ortho and para positions; the para product is major because the ortho positions are crowded by the chlorine atom.

Why the other options are incorrect

• Option (2) Nucleophilic substitution reaction — Incorrect. In this type a nucleophile replaces the halogen, e.g. chlorobenzene with NaOH at 623 K and 300 atm gives phenol. Here the chlorine stays on the ring and an electrophile replaces a hydrogen.

• Option (3) Electrophilic addition reaction — Incorrect. This is typical of alkenes, e.g. \( \ce{CH2=CH2 + HBr -> CH3CH2Br} \). The benzene ring does not add the reagent; it keeps its aromatic sextet by losing \( \ce{H+} \).

• Option (4) Nucleophilic addition reaction — Incorrect. This is typical of aldehydes and ketones, e.g. the addition of HCN to the C=O group; there is no carbonyl group here.

Note: It seems that there is a mistake in the original NTA paper. The reagent in the reaction is printed as \( \ce{CHCl3} \) (chloroform); it should be \( \ce{CH3Cl} \) (methyl chloride), since only methyl chloride gives 1-chloro-2-methylbenzene and 1-chloro-4-methylbenzene.

NCERT (2026-27 edition):
Electrophilic Substitution Reactions – “Haloarenes undergo the usual electrophilic reactions of the benzene ring such as halogenation, nitration, sulphonation and Friedel-Crafts reactions. Halogen atom besides being slightly deactivating is o, p- directing; therefore, further substitution occurs at ortho- and para- positions with respect to the halogen atom.”

Friedel-Crafts Reaction