Question

_____ reagent is used in the xanthoproteic test for proteins.

• A. Conc. HCl
• B. Conc. $H_{2}SO_{4}$
• C. Conc. $HNO_{3}$
• D. Conc. $H_{3}PO_{4}$

Hint:

Xantho = Yellow; Nitric acid ($HNO_{3}$) makes aromatic proteins yellow.

Answer 1

The Correct Option is C

Step 1: Concept
The xanthoproteic test is used to detect the presence of proteins containing aromatic amino acids (like tyrosine or tryptophan).

Step 2: Meaning
The reaction involves the nitration of the benzene ring in the amino acid side chain.

Step 3: Analysis
Concentrated nitric acid ($HNO_{3}$) reacts with the aromatic rings to form a yellow-colored nitro compound, which turns orange upon the addition of an alkali.

Step 4: Conclusion
Therefore, concentrated nitric acid is the essential reagent for this test.

Final Answer: (C)