The reaction between propanoyl chloride and benzene is an example of acylation - AQA - A-Level Chemistry - Question 26 - 2019 - Paper 3

The correct representation of the mechanism involves the formation of an acylium ion from propanoyl chloride. In this step, the carbonyl group in propanoyl chloride facilitates the creation of a resonance-stabilized ion, allowing it to effectively electrophilically attack the benzene ring. This results in the substitution of a hydrogen atom on the benzene ring with the acyloxy group. Representation C accurately reflects this process by showing the formation of the acylium ion and its subsequent attack on the benzene ring.