Monosaccharides are simple sugars with a single ring structure

Steps:

• Define monosaccharide as a carbohydrate that cannot be hydrolyzed into simpler sugars, typically with 3-7 carbons.
• Identify ribose (1) as a 5-carbon aldopentose used in RNA, a monosaccharide.
• Identify glucose (2) as a 6-carbon aldohexose, the primary energy source, a monosaccharide.
• Identify deoxyribose (3) as a modified 5-carbon pentose in DNA, a monosaccharide.
• Identify sucrose (4) as a disaccharide formed by glucose and fructose linked by a glycosidic bond.

Why A is correct:

• Ribose, glucose, and deoxyribose match the monosaccharide definition as unhydrolyzable single-unit sugars with formulas like C5H10O5 or C6H12O6.

Why the others are wrong:

• B includes sucrose, a disaccharide (C12H22O11) that hydrolyzes into two monosaccharides.
• C excludes glucose, a classic monosaccharide essential in metabolism.
• D includes sucrose (disaccharide) and excludes ribose and deoxyribose (monosaccharides).

Final answer: A