Functional groups are molecules with specific atoms and have their own chemical properties when attached to some other substances. Glucose is a simple sugar and has an aldehyde group (CHO) as its functional group. The presence of CHO in it makes it be present in food without any harmful impacts. On the other hand, hexanoic acid has COOH (carboxylic group) as its functional group. COOH group has a tendency to donate its protons and become ionized. It is toxic as it is reactive and tends to affect the pH of the food or solution in which it is present.
