Compound "A" reacts with \(NaNO_2\) and \(HCl\) to give a diazonium salt, which on reaction with N,N-dimethylaniline produces methyl orange. What is the compound "A"?
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Methyl orange is made by coupling a diazonium salt of an aromatic amine that also bears a sulphonic acid group with N,N-dimethylaniline.
Alternative approach: build methyl orange's structure: $-O_3S-C_6H_4-N=N-C_6H_4-N(CH_3)_2$. One half comes from N,N-dimethylaniline. The other half must have arisen from a diazonium ion $-O_3S-C_6H_4-N_2^+$. Working backward, replacing $-N_2^+$ with $-NH_2$ gives sulphanilic acid. None of the other choices carry a free aromatic $-NH_2$ group at all.