Concept:The purple colour is produced by the Biuret test, which is used to detect proteins.
Explanation:When a food substance is treated with sodium hydroxide (
NaOH) solution and one drop of copper sulphate (
CuSO4) solution, a purple colour indicates a positive result.
This purple colour forms because copper ions react with peptide bonds in the food substance under alkaline conditions.
Only proteins contain peptide bonds that give this reaction.
Carbohydrates, fats, and sugars do not contain such peptide bonds, so they do not produce this purple colour with the same reagents.
Hence, the food substance showing a purple colour is likely a protein.
Answer:C. protein