Identify 'A' from the following compounds:

The correct answer is Option (2) → Propiophenone (ethyl phenyl ketone, C₆H₅COC₂H₅)

Benzene treated with an acid chloride in the presence of anhydrous \( \ce{AlCl3} \) gives the corresponding ketone. This is Friedel-Crafts acylation. \( \ce{AlCl3} \) generates the acylium ion \( \ce{C2H5CO^{+}} \), which substitutes a hydrogen of the ring:

    \( \ce{C6H6 + C2H5COCl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{C6H5COC2H5 + HCl} \)

So A is 1-phenylpropan-1-one.

Why the other options are incorrect

• Option (1) C₆H₅CH₂CH₂COCl — Incorrect. This product would need the ring to bond to the ethyl end of propanoyl chloride. In acylation, \( \ce{AlCl3} \) removes \( \ce{Cl^-} \) to give the acylium ion \( \ce{C2H5-C#O^+} \), and the ring bonds to the carbonyl carbon, so no –COCl group can remain.

• Option (3) Benzoic acid — Incorrect. Benzoic acid is made by oxidising a side chain, for example toluene with alkaline \( \ce{KMnO4} \). No oxidising agent is present here, and the product keeps the ethyl group of the acid chloride.

• Option (4) Acetophenone — Incorrect. Acetophenone (\( \ce{C6H5COCH3} \)) would need ethanoyl chloride; here the reagent is propanoyl chloride, \( \ce{C2H5COCl} \).

NCERT (2026-27 edition):
Preparation of Ketones – …