Which of the following is the IUPAC name for C4H9OH?

The correct identification of C4H9OH is indeed butanol. This molecule contains four carbon atoms (indicated by 'C4') and is recognized as an alcohol due to the presence of the -OH hydroxyl group. In IUPAC nomenclature, the longest carbon chain is counted to determine the base name of the compound, and in this case, a four-carbon straight-chain alcohol with an -OH group is named butanol.

The prefix 'but-' signifies the presence of four carbon atoms, while the suffix '-ol' indicates that the molecule is an alcohol due to the hydroxyl functional group.

While propanol, methanol, and ethanol could imply other structures and formulas, they refer to compounds with three, one, and two carbon atoms respectively. Propanol (C3H8O) has a three-carbon backbone, methanol (CH3OH) consists of a one-carbon structure, and ethanol (C2H5OH) contains two carbons. None of these would fit the molecular formula C4H9OH, confirming that butanol is the correct name based on the structure and formula provided.