What is the defining feature of a triol?

A triol is specifically characterized by the presence of three hydroxyl (-OH) functional groups attached to its carbon backbone. This definition aligns perfectly with the description provided in the correct answer, as it highlights the number of hydroxyl groups that define triols. Each hydroxyl group contributes to the compound's reactivity and properties, such as solubility and boiling point.

Understanding that triols are a subset of alcohols, it's also important to note that not all alcohols have three hydroxyl groups. For example, monohydric alcohols contain only one hydroxyl group, while diols contain two. The unique structural feature of triols sets them apart in chemical behavior and applications.

The other options focus on different aspects of alcohols. While alcohols with two carbon atoms describe a specific category of alcohols (ethanol being a common example), it does not pertain to the number of hydroxyl groups. The term "fully saturated" relates to the types and numbers of chemical bonds in organic molecules, which is not definitive for triols, as they can also be unsaturated. Lastly, the reference to a ketone group is unrelated since ketones and alcohols are distinct functional groups, with the latter specifically defined by hydroxyl