This reaction sequence involves a series of transformations:
Chlorination: Chlorination of the ethylbenzene ring will occur preferentially at the para position due to the activating effect of the ethyl group and the deactivating meta-directing nature of the nitro group.
Reduction: Reduction of the nitro group (-NO2) to an amino group (-NH2) using tin and hydrochloric acid (Sn/HCl).
Diazotization: The amino group is converted into a diazonium group (-N2+) using sodium nitrite and hydrochloric acid (NaNO2/HCl) at a low temperature (273-278 K).
Sandmeyer Reaction: The diazonium group is replaced by an iodide (I) using potassium iodide (KI) via a Sandmeyer reaction. This replacement occurs at the same position as the original amino group (and thus the nitro group). Thus, we have 4-iodo-1-ethyl-2-chlorobenzene.