Ans. is 'b' i.e., Amino acids Important chemicai reactions of amino acidso Fol(owing are some important chemical reactions.Reaction used to determine amino acid sequence in polypeptide chain : -Generally, amino terminal (N-tenninal) of amino acid is tagged with some reagent. It is split offby hydrolysis and tagged amino acid is identified. The reaction is, then, repeated with new N-terminal of subsequent amino acid and so on. The two reactions are used for identification of amino acid sequence : -Sanger's reaction : - Uses Sanger's reagent (1 -fluoro-2,4-dinitrobenzene) to tag amino terminal.Edman's reaction : - Uses Edman's reagent (phenylisothiocyanate) to tag amino terminal.Reaction used to identification of individual or group of amino acids : - These reactions are frequently used for qualitative detection and quantitative measurement of various amino acids.Xin hydrin test0 : - All a-amino acids.Xanthophoretic reaction : - Aromatic amino acids Q (Tyrosine, try ptophan, phenylalanine).Millan's test Q (Miilon-Nasse reaction): - Tyrosine Q (phenol group of tyrosine). Therefore millon's test is positive in tyrosinosis Q.Aldehyde test: - Tryptophan (indole ring)Hopkins-cole reaction : - Tryptophan (indole ring)Sakaguch's reaction : - Arginine (guanidinium group of arginine).Sulphur test: - Cysteine (sulphydryl group)Nitroprusside test: - Cysteine (sulphydryl group)Pauly's test: - Histidine (imidazole group)Biuret reaction : - Peptide bondDiazo reaction Q (Pauli's) : - Histidine or tyrosine.