Question

Which of the following is correct about proteins?

• A. Proteins give a violet colour with alkaline $CuS{O}_4$ solution
• B. Proteins give a purple colour on boiling with dilute ninhydrin solution
• C. Proteins give a yellow colour on boiling with $HN{O}_3$
• D. All of the above

Answer 1

The correct option is D All of the above

Option (D) is correct.
(A) Proteins gives a violet colour with alkaline $CuS{O}_4$ solution. This color change is dependent on the number of peptide bonds in the solution, so the more protein, the more intense the change. This is called biuret test for proteins.
(B) Proteins gives a purple colour on boiling with dilute ninhydrin solution forming ninhydrin coloured complex.
(C) Proteins gives yellow colour on boiling with $HN{O}_3$, forming yellow coloured nitro derivatives.