See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Concept: Isomers of D-Glucose (C6H12O6) are compounds that share the same molecular formula but differ in structural or stereochemical arrangement. We must identify which of the listed compounds are isomers (constitutional, structural, or stereoisomers) of D-Glucose. Step 1: Determine the molecular formula of D-Glucose. D-Glucose is a hexose (6-carbon sugar) with molecular formula C6H12O6. Step 2: Check each compound: - D-Mannose: C6H12O6 (aldohexose) — same molecular formula as D-Glucose. It differs only at C-2 (epimer). This IS an isomer. ✓ - D-Fructose: C6H12O6 (ketohexose) — same molecular formula as D-Glucose. It is a structural (constitutional) isomer (ketose vs aldose). This IS an isomer. ✓ - D-Gulose: C6H12O6 (aldohexose) — same molecular formula as D-Glucose. It is a stereoisomer. This IS an isomer. ✓ - D-Idose: C6H12O6 (aldohexose) — same molecular formula as D-Glucose. It is a stereoisomer. This IS an isomer. ✓ - D-Galactose: C6H12O6 (aldohexose) — same molecular formula as D-Glucose. It is a stereoisomer (epimer at C-4). This IS an isomer. ✓ - D-Arabinose: C5H10O5 (aldopentose) — different molecular formula (5 carbons). This is NOT an isomer of D-Glucose. ✗ - D-Ribose: C5H10O5 (aldopentose) — different molecular formula (5 carbons). This is NOT an isomer of D-Glucose. ✗ Step 3: Count the isomers. D-Mannose, D-Fructose, D-Gulose, D-Idose, and D-Galactose = 5 compounds. D-Arabinose and D-Ribose are pentoses (C5H10O5) and do not share the same molecular formula as D-Glucose, so they are not isomers. Therefore, the correct answer is 5.