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Question:

Considering all possible isomeric ketones, including stereoisomers of a compound having a molecular weight of 100. All these isomers are independently reacted with NaBH4. The total number of ketones that give a racemic product(s) is/are: [Note: stereoisomers are also reacted separately]

Solution:

CnH2nO → 12×n + 2×n × 1 + 16 = 100 → n = 6
1st ketone: the R and S both reacts separately with NaBH4 to form diastereomeric pair.
The possible no. of isomers of C6H12O are shown above in the figure.
Hence the correct answer is 5.