See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: When a benzene ring with substituents undergoes electrophilic aromatic substitution (chlorination), the number of distinct monochloroderivatives equals the number of chemically non-equivalent hydrogen positions on the ring. Step 1 - Analyze o-xylene (1,2-dimethylbenzene): The two methyl groups are on adjacent carbons. By symmetry, there are only three sets of unique ring hydrogens: position 3 (or 6, equivalent by symmetry), position 4 (or 5, equivalent by symmetry), and... actually positions 3 and 6 are equivalent, and positions 4 and 5 are equivalent, giving only 2 unique monochloro products on the ring (plus one on the methyl CH3, but for ring chlorination: 2 unique positions). Counting all positions including methyl: 3 distinct products. Wait - re-examining carefully: o-xylene has H at positions 3, 4, 5, 6. By the mirror plane, H3=H6 and H4=H5, giving 2 unique ring positions, hence 2 ring monochloroderivatives. Total (including side chain) = 3, but conventionally ring substitution is considered, giving 2. Step 2 - Analyze m-xylene (1,3-dimethylbenzene): The two methyl groups are at positions 1 and 3. Ring hydrogens are at positions 2, 4, 5, and 6. By the symmetry plane bisecting C2 and C5: H4=H6 (equivalent), H2 is unique, H5 is unique. This gives three unique ring hydrogen environments: H2 (between the two methyls), H4/H6 (adjacent to one methyl), and H5 (para to one methyl, meta to the other). Therefore m-xylene gives THREE distinct monochloroderivatives upon ring chlorination. Step 3 - Analyze p-xylene (1,4-dimethylbenzene): All four ring hydrogens are equivalent by symmetry, giving only ONE unique ring monochloroderivative. Step 4 - Eliminate wrong options: o-xylene gives 2 unique ring monochloro products; p-xylene gives 1; d is incorrect as xylene clearly can give monochloro derivatives. Only m-xylene gives exactly 3 different monochloroderivatives. Therefore, the correct answer is B.