Explanation:The Friedel-Crafts acylation reaction is a common method for preparing ketones like acetophenone. In this reaction, benzene reacts with an acyl chloride (such as acetyl chloride) in the presence of a Lewis acid catalyst (like $\mathrm{A} 1 \mathrm{Cl}$ ) to form acetophenone.

The reaction is as follows:
\(\mathrm{C}_6 \mathrm{H}_6+\mathrm{CH}_3 \mathrm{COCl} \xrightarrow{\text { anhydrous aluminium chloride }} \mathrm{C}_6 \mathrm{H}_5 \mathrm{COCH}_3+\mathrm{HCl}\)
This reaction introduces the acetyl group $\left(\mathrm{COCH} 3 \mathrm{COCH}_3\right)$ to the benzene ring, forming acetophenone.