Which functional group can always be found in a carbohydrate molecule?

• A. Phosphate group (\(-PO_4^{2-}\))
• B. Sulfhydryl group (\(-SH\))
• C. Amino group (\(-NH_2\))
• D. Hydroxyl group (\(-OH\))

Answer: (D)

Verified step by step guidance

1. Understand the structure of carbohydrates: Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms, typically in a ratio of 1:2:1. They are classified as monosaccharides, disaccharides, or polysaccharides based on the number of sugar units.
2. Identify the functional groups commonly found in carbohydrates: Carbohydrates contain specific functional groups that contribute to their chemical properties. These include hydroxyl groups ( $-{\mathrm{OH}}_{}$), aldehyde groups ( $-{\mathrm{CHO}}_{}$), and ketone groups ( $-{\mathrm{CO}}_{}$).
3. Focus on the hydroxyl group ( $-{\mathrm{OH}}_{}$): Hydroxyl groups are present in all carbohydrate molecules. They are responsible for the molecule's ability to form hydrogen bonds, which contribute to solubility in water and reactivity in biochemical processes.
4. Compare the other functional groups listed in the problem: Phosphate groups ( $-{\mathrm{PO}}_4$), sulfhydryl groups ( $-{\mathrm{SH}}_{}$), and amino groups ( $-{\mathrm{NH}}_2$) are not characteristic of carbohydrates. These groups are more commonly found in other biomolecules such as nucleotides, proteins, and lipids.
5. Conclude that the hydroxyl group ( $-{\mathrm{OH}}_{}$) is the functional group always present in carbohydrate molecules, making it the correct answer to the problem.