See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Concept: In mutarotation, the observed optical rotation of an equilibrium mixture is the weighted average of the optical rotations of the individual anomers. Let x = fraction of alpha-form in the equilibrium mixture. Then (1 - x) = fraction of beta-form. The weighted average equation: x * (+150.7°) + (1 - x) * (+52.8°) = +80.2° Expanding: 150.7x + 52.8 - 52.8x = 80.2 Collecting x terms: (150.7 - 52.8)x = 80.2 - 52.8 97.9x = 27.4 x = 27.4 / 97.9 x ≈ 0.2799 ≈ 28% So the percentage of alpha-form is approximately 28%. Why other options fail: - 32%: Would give 0.32 * 150.7 + 0.68 * 52.8 = 48.224 + 35.904 = 84.128°, not 80.2° - 68%: Would give 0.68 * 150.7 + 0.32 * 52.8 = 102.476 + 16.896 = 119.37°, not 80.2° - 72%: Would give 0.72 * 150.7 + 0.28 * 52.8 = 108.504 + 14.784 = 123.29°, not 80.2° Therefore, the correct answer is A.