Disaccharides with Free Anomeric Carbon

Steps:

• Identify disaccharides as carbohydrates formed by two linked monosaccharides via glycosidic bonds.
• Recognize reducing sugars as those with at least one free anomeric carbon that can open to form an aldehyde or ketone group.
• Evaluate options: fructose and glucose are monosaccharides; maltose links two glucoses with one free anomeric carbon; sucrose links glucose and fructose with both anomeric carbons bound.
• Confirm maltose fits both criteria as a disaccharide and reducing sugar.

Why C is correct:

• Maltose consists of two glucose units linked by an α-1,4 glycosidic bond, leaving one anomeric carbon free to act as a reducing agent.

Why the others are wrong:

• A. Fructose is a monosaccharide, not a disaccharide.
• B. Glucose is a monosaccharide, not a disaccharide.
• D. Sucrose is a disaccharide, but non-reducing due to both anomeric carbons forming the glycosidic bond.

Final answer: C