Benzyne mechanism replaces Br with OH in bromochlorobenzene

Steps:

• Identify J as bromochlorobenzene (C₆H₄BrCl), an aryl dihalide unreactive to direct SNAr.
• Hot concentrated NaOH in ethanol generates strong base (OH⁻/EtO⁻) that abstracts ortho-H to Br, eliminating Br⁻ to form chlorobenzyne intermediate.
• OH⁻ adds to the electron-deficient benzyne triple bond, followed by protonation, yielding chlorophenol.
• Br eliminates preferentially over Cl due to better leaving group ability (Br > Cl), so Cl remains intact.

Why B is correct:

• B shows the skeletal formula of chlorophenol (C₆H₄ClOH), the substitution product where only Br is replaced by OH.

Why the others are wrong:

• A shows bromophenol, but Cl is not eliminated preferentially over Br.
• C shows chlorophenyl ethyl ether, but OH⁻ is the dominant nucleophile, not EtO⁻.
• D shows resorcinol (dihydroxybenzene), but excess base replaces only the more reactive Br, not both halides.

Final answer: B