JEE Advanced 2025 Paper 1, Chemistry Section 4 Q3: Principles Of Qualitative Analysis

(P) The compound has a free $\alpha$-amino group and a phenolic –OH. It would give a positive ninhydrin test (free $\alpha$-amino acid character) and the phenolic group gives a violet colour with FeCl${}_3$. Matches (2).

(Q) Both nitrogens are masked (one acetyl, one amide), and the carboxyl is esterified. Complete hydrolysis liberates the free amino acids, which then give a positive ninhydrin test. No phenolic OH is present, so the phthalein dye test is negative. Matches (5).

(R) On warming or basification, anilinium chloride frees aniline, which couples with a phenyl diazonium salt at the para-position to form p-aminoazobenzene, a yellow azo dye. Matches (1).

(S) An arylhydrazine condenses with the aldehyde carbonyl of glucose to give a hydrazone (and on excess hydrazine an osazone). Matches (3).

$\therefore$ P$\to$2, Q$\to$5, R$\to$1, S$\to$3. Option (B).