Which of the following is a characteristic of alcohols?

In organic chemistry, alcohols are defined by their functional group, which is the hydroxyl group (-OH). This characteristic is what distinguishes alcohols from other types of organic compounds. The presence of the hydroxyl group contributes to many of the unique physical and chemical properties of alcohols, including their polarity and the ability to form hydrogen bonds, which in turn greatly influences their boiling and melting points.

The carbonyl group, which is characteristic of aldehydes and ketones, does not pertain to alcohols, separating this option from the correct answer. Similarly, alcohols are not required to be aromatic; they can either be aliphatic or aromatic depending on the structure of the compound. Lastly, while alcohols often have higher boiling points compared to their corresponding alkanes due to their ability to engage in hydrogen bonding through the hydroxyl group, this is not a defining characteristic of all alcohols but rather a comparative observation with other hydrocarbon classes.

Thus, the defining feature of alcohols is their hydroxyl groups, making that answer the most accurate choice.