See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: When an aromatic compound undergoes electrophilic aromatic nitration, the number of mononitration products depends on the symmetry of the molecule and the directing effects of the substituents already present. Step 2 - Analyze each C8H10 isomer for the number of distinct mononitration products: (a) Ethylbenzene: The ethyl group is an ortho/para director. Nitration can occur at ortho (2 equivalent positions), para (1 position), and meta (2 equivalent positions but less favored). Considering symmetry, ortho gives one product, para gives one product, and meta gives one product — that is 3 distinct products. Does not fit. (b) Ortho-xylene (1,2-dimethylbenzene): The two methyl groups are both ortho/para directors. The ring positions available are C3, C4, and C5 (C6 is equivalent to C3 by symmetry, and C1/C2 are occupied). By the symmetry of ortho-xylene: position 3 and position 6 are equivalent; position 4 and position 5 are equivalent. Wait — let us label carefully. In 1,2-dimethylbenzene, methyls at C1 and C2. Free positions: C3, C4, C5, C6. Due to the mirror plane: C3 ≡ C6, and C4 ≡ C5. So there are only 2 distinct positions for nitration (3/6 and 4/5), giving exactly 2 mononitration products. This fits the evidence perfectly. (c) Meta-xylene (1,3-dimethylbenzene): Methyls at C1 and C3. Free positions: C2, C4, C5, C6. By symmetry: C2 is unique (between the two methyls), C4 ≡ C6 (ortho to one methyl, para to the other), and C5 is unique (para to both... actually between them on the far side). So positions C2, C4(=C6), and C5 — that gives 3 distinct products. Does not fit. (d) Para-xylene (1,4-dimethylbenzene): Methyls at C1 and C4. Free positions: C2, C3, C5, C6. By symmetry all four are equivalent (C2 ≡ C3 ≡ C5 ≡ C6). Only 1 distinct mononitration product. Does not fit. Step 3 - Conclusion: Only ortho-xylene gives exactly two mononitration products, matching the experimental observation. Therefore, the correct answer is B.