Which functional group is characterized by a carbon atom double-bonded to an oxygen atom ($C=O$) and single-bonded to a hydroxyl group ($\mathrm{OH}$)?

• A. Hydroxyl group ($\mathrm{OH}$)
• B. Amino group ($\mathrm{NH}{2}_{}$)
• C. Carboxyl group ($\mathrm{COOH}$)
• D. Carbonyl group ($\mathrm{CO}$)

Answer: (C)

Verified step by step guidance

1. Identify the functional groups listed in the problem: Hydroxyl group, Amino group, Carboxyl group, and Carbonyl group.
2. Understand the structural characteristics of each functional group: A hydroxyl group consists of an -OH bonded to a carbon atom, an amino group consists of a nitrogen atom bonded to hydrogen atoms, a carboxyl group consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group, and a carbonyl group consists of a carbon atom double-bonded to an oxygen atom.
3. Focus on the description given in the problem: A carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group.
4. Match the description to the correct functional group: The description matches the structure of a carboxyl group, which is represented as $\left(R\right)-C=O-\mathrm{OH}$.
5. Conclude that the functional group characterized by a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group is the carboxyl group.