What is the IUPAC name for CH3-CO-CH2-CH3?

The molecular formula CH3-CO-CH2-CH3 represents a ketone, specifically butan-2-one. To determine the IUPAC name, we need to follow the nomenclature rules for naming carbon chains that contain functional groups.

In this structure, you have a four-carbon chain (butane) where a carbonyl group (C=O) is located at the second carbon position. The carbonyl group is characteristic of ketones, and because it is situated between two carbon atoms in a four-carbon chain, it is designated as butan-2-one. The "2" in the name indicates the position of the carbonyl group.

The other options do not apply to this compound. Butanoic acid refers to a carboxylic acid, which contains a -COOH group rather than a ketone. 2-Trifluoromethylbutane suggests the presence of trifluoromethyl (-CF3) substituents, which is not present in the structure provided. Lastly, acetone is a common name for propan-2-one, which has a three-carbon chain and differs from the four-carbon chain here.