The carboxylic acid group (-COOH) includes a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (-OH).
Now, let's analyze the compounds:
Aspirin (acetylsalicylic acid) features a carboxylic acid group attached to a benzene ring and an ester group; thus, it has a -COOH group.
Ethanol (CH\(_3\)CH\(_2\)OH) only possesses a hydroxyl group (-OH), not a -COOH group.
Acetone (CH\(_3\)COCH\(_3\)) is a ketone, with a carbonyl group (C=O) but no -COOH group.
Formaldehyde (HCHO) is an aldehyde with a -CHO group, which is not a -COOH group.
Consequently, only Aspirin contains the carboxylic acid (-COOH) group.