What differentiates a ketone from an aldehyde?

A ketone and an aldehyde are both carbonyl-containing compounds, but the key difference lies in the location of the carbonyl group, which is the functional group characterized by a carbon atom double-bonded to an oxygen atom.

In aldehydes, the carbonyl group is always located at the end of the carbon chain. This means that the aldehyde can be identified by its structure, which includes a carbonyl group directly bonded to a carbon atom that is also attached to at least one hydrogen atom. For example, in formaldehyde, the carbonyl is at the terminal position, making it an aldehyde.

In contrast, ketones have their carbonyl group situated within the carbon chain. This means that the carbonyl is flanked by two other carbon atoms on either side, which distinguishes ketones from aldehydes. For instance, in acetone, the carbonyl group is surrounded by two carbon groups, confirming its classification as a ketone.

Therefore, the location of the carbonyl group is essential for differentiating between aldehydes and ketones, which makes it the correct answer to the question. The other options do not directly explain the fundamental structural difference that defines these two types of compounds.