D-mannose is the C-2 epimer of:

Correct answer: (d) D-glucose

Explanation

Epimers are sugars that differ in the arrangement of groups around only one carbon atom. D-mannose and D-glucose are both aldohexoses (six-carbon sugars with an aldehyde group) and differ only at carbon 2, so D-mannose is the C-2 epimer of D-glucose.

• D-galactose is the C-4 epimer of D-glucose.
• D-fructose is a ketohexose (with a ketone group), an isomer of glucose but not an epimer.
• D-erythrose has only four carbons.