Answer:
Carboxyl functional group.
Step-by-step explanation:
Carboxyl functional group is the feature or characteristic which us absent in the monosaccharide. The carboxyl group is an organic, functional group comprising of a carbon atom which is double-bonded to an oxygen atom and have singly bond with a hydroxyl group. In other words we can say that it is a carbonyl group (C=O) that has a hydroxyl group (O-H) which is attached to the carbon atom.