See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Step 1: Determine the number of stereocenters in aldoheptose. An aldoheptose is a 7-carbon aldose sugar. The carbonyl (aldehyde) is at C1, and the stereocenters are at C2, C3, C4, C5, C6, giving 5 stereocenters. Number of stereoisomers = 2^5 = 32. Step 2: Determine the number of stereocenters in ketoheptose. A ketoheptose is a 7-carbon keto sugar. The carbonyl (ketone) is conventionally at C2, and the stereocenters are at C3, C4, C5, C6 (C1 and C7 are terminal CH2OH groups, not stereocenters), giving 4 stereocenters. Number of stereoisomers = 2^4 = 16. Step 3: Calculate the ratio a/b. a = 32 (stereoisomers of aldoheptose), b = 16 (stereoisomers of ketoheptose). a/b = 32/16 = 2/1. Step 4: Why other options fail. Option (a) 1/2 would imply ketoheptose has more stereoisomers than aldoheptose, which is incorrect since aldoheptose has one more stereocenter. Option (c) 4/1 would require a/b = 4, which would need a difference of 2 stereocenters, not 1. Option (d) 1/4 is the inverse and incorrect. Therefore, the correct answer is B.