See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

To convert benzene into meta-chlorobromobenzene, we need Cl and Br substituents in a meta relationship on the benzene ring. Meta directors must be used to achieve this regiochemistry. Step-by-step reasoning for answer (d): 8 then 2 then 4 then 3 then 9 Step 1 (Reagent 8): Nitration of benzene using HNO3(conc.) + H2SO4(conc.) and heat gives nitrobenzene. The nitro group is a meta director. Step 2 (Reagent 2): Electrophilic aromatic chlorination of nitrobenzene using Cl2 + FeCl3. Because the nitro group is a meta director, chlorine is introduced at the meta position relative to -NO2, giving meta-chloronitrobenzene. Step 3 (Reagent 4): Reduction of the nitro group to an amine using H2 with Pt catalyst gives meta-chloroaniline. This converts -NO2 to -NH2, which is needed for the Sandmeyer reaction. Step 4 (Reagent 3): Diazotization of the amine using NaNO2 + H3O(+) at 0°C converts -NH2 to a diazonium salt (-N2(+)), giving meta-chlorobenzenediazonium salt. Step 5 (Reagent 9): Sandmeyer reaction using Cu2Br2 + HBr replaces the diazonium group with bromine, giving meta-chlorobromobenzene. Why other options fail: - Option (a): Only uses sulfonation, chlorination, and PBr3 — no pathway to introduce both Cl and Br in meta relationship. - Option (b): Starts with chlorination (ortho/para director installed first), then nitration would go ortho/para to Cl, not giving clean meta product; also the sequence does not correctly build meta-chlorobromobenzene. - Option (c): Uses reagent 10 (acetylation with acetic anhydride/pyridine) which is used to protect an amine — this sequence introduces unnecessary complexity and does not correspond to a clean synthesis from benzene to meta-chlorobromobenzene using the given reagents in a logical order. The key concept is: introduce the meta-directing nitro group first, place Cl meta to it, reduce the nitro to amine, diazotize, then Sandmeyer to install Br where the diazonium was (which is meta to Cl). Therefore, the correct answer is d.