Which of the following best describes an alcohol?

An alcohol is defined as a compound that contains a hydroxyl group (-OH) attached to a carbon atom. This functional group is what characterizes alcohols and distinguishes them from other types of organic compounds. The presence of the hydroxyl group not only defines the structure of alcohols but also significantly influences their chemical properties, including their solubility in water and their reactivity.

In contrast, compounds that contain a carbonyl group (C=O), which is characteristic of aldehydes and ketones, do not fall under the category of alcohols. Similarly, hydrocarbons that lack functional groups do not represent the structure or function of alcohols either. Additionally, while some alcohols can exhibit acidic behavior in certain contexts, not all alcohols are classified as acidic; thus, this option does not accurately define the essential characteristics of alcohols. Consequently, the best descriptor of an alcohol is a compound containing a hydroxyl group.