A sugar carrying an aldehyde functional group is classified as:

1. Monosaccharides are sorted by which carbonyl-containing group they carry. 2. A sugar with a ketone group is a ketose. 3. A sugar with an aldehyde group of structure R-CHO is an aldose. 4. Pentose and hexose are wrong because those names count carbons, not functional groups. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 3 'Biological Macromolecules', sections 3.1-3.5_