AIIMS 2019 Biology Proteins MCQ Question

The reaction of proteins with ninhydrin (option A) produces Ruhemann's purple, a deep blue-purple color, due to the formation of a complex between ninhydrin and the amino acids released upon protein hydrolysis. This reaction is commonly used to detect free amino acids and proteins in biochemical assays. In contrast, Cu²⁺ (option B) typically forms a blue complex with proteins but does not yield Ruhemann's purple; H₂O₂ (option C) is not directly involved in protein detection and does not produce this color change. Thus, ninhydrin is specifically significant for identifying proteins through this distinctive color reaction.