Question

Biuret test is not given by:

• A. Carbohydrates
• B. Polypeptides
• C. Urea
• D. Proteins

Hint:

Biuret test is used to detect peptide bonds in proteins and polypeptides. Carbohydrates do not contain peptide linkages, hence do not respond to the Biuret test.

Answer 1

The Correct Option is A

Step 1: Understand the Biuret test
The Biuret test is a chemical test used to detect the presence of peptide bonds (–CO–NH–) in a substance. It gives a violet or purple-colored complex when:

• Two or more peptide bonds are present
• The sample contains proteins or polypeptides

Step 2: Analyze each option

• Proteins — made up of many peptide bonds → gives Biuret test
• Polypeptides — short chains of amino acids → give Biuret test
• Urea — a simple molecule with an amide group, can give a weak positive test under certain conditions
• Carbohydrates — made of carbon, hydrogen, and oxygen but no peptide bonds → do not give Biuret test

Step 3: Conclusion
Only carbohydrates lack the functional group required (peptide bond) to produce a positive Biuret test result. \[ \boxed{\text{Carbohydrates do not give the Biuret test.}} \]