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

• A. Ketone
• B. Aldehyde
• C. Carboxylic acid
• D. Ether

Answer: (C)

Verified step by step guidance

1. Identify the functional group described: a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group.
2. Recognize that this description matches the structure of a carboxylic acid.
3. Understand that a carboxylic acid has the general formula \( \text{R-COOH} \), where \( \text{R} \) is a hydrocarbon group, \( \text{C} \) is the carbon atom, \( \text{O} \) is the oxygen atom, and \( \text{OH} \) is the hydroxyl group.
4. Compare this structure to other functional groups: a ketone has a carbonyl group (\( \text{C=O} \)) bonded to two carbon atoms, an aldehyde has a carbonyl group bonded to at least one hydrogen atom, and an ether has an oxygen atom bonded to two carbon atoms.
5. Conclude that the functional group described is a carboxylic acid, as it uniquely contains both a carbonyl group and a hydroxyl group bonded to the same carbon atom.