The correct option is -COOH.
Explanation
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In organic chemistry, the classification of compounds is primarily based on the presence of these specific functional groups.
Option Analysis:
- -COOH is correct: The group -COOH is known as the carboxyl group. It consists of a carbonyl group (>C=O) and a hydroxyl group (-OH) attached to the same carbon atom. This is the defining functional group for carboxylic acids (e.g., Ethanoic acid).
- -OH is incorrect: The group -OH is the hydroxyl group, which is the characteristic functional group for alcohols.
- -CHO is incorrect: The group -CHO represents the aldehyde group.
- >C=O is incorrect: The group >C=O represents the carbonyl group. While it is a component of carboxylic acids, aldehydes, and esters, when used to classify a specific family of compounds where the carbon is bonded to two other carbons, it refers to ketones.
Key Takeaway: The functional group responsible for the acidity and chemical properties of carboxylic acids is the carboxyl group (-COOH).