Which of the following functional groups is present in all amino acids?

• A. Ketone group ($R-C=O-R\text{'}$)
• B. Carboxyl group ($-C=O-OH$)
• C. Hydroxyl group ($-OH$)
• D. Aldehyde group ($-CH=O$)

Answer: (B)

Verified step by step guidance

1. Understand the structure of an amino acid: Amino acids are organic compounds that contain both an amino group (-NH₂) and a carboxyl group (-COOH).
2. Identify the functional groups listed in the problem: Ketone group (C=O), Carboxyl group (-COOH), Hydroxyl group (-OH), and Aldehyde group (CHO).
3. Recall that the carboxyl group (-COOH) is a defining feature of amino acids, as it is present in all amino acids.
4. Compare the functional groups: The ketone group, hydroxyl group, and aldehyde group are not present in all amino acids, whereas the carboxyl group is.
5. Conclude that the carboxyl group is the functional group present in all amino acids, as it is essential for their structure and function.