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UPSC Combined Geo-Scientist

Chemist

  • 2 objective papers
  • 120 questions each
  • 2 h per paper
  • 100 + 300 marks

Prelims Paper II covers chemistry.

UPSC Combined Geo-Scientist, Prelims · 2020 · Paper II, Chemistry · Q92 of 120

Geo-Scientist Prelims 2020 Chemistry Q92: The total number of optical isomers possible for cholesterol is:

QuestionStereochemistry / counting isomers

The total number of optical isomers possible for cholesterol is:

UPSC Combined Geo-Scientist Prelims 2020 Paper II (Chemistry), Q92: figure printed with the question
  1. (a) 128
  2. (b) 256
  3. (c) 64
  4. (d) 512

Answer: (b) 256

Cholesterol has 8 stereocentres (C3, C8, C9, C10, C13, C14, C17, C20). Maximum stereoisomers = 2⁸ = 256 → (b). Only one occurs naturally.

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