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JEE Advanced levelSingle correct optionDifficulty 3 of 3pl214

A 8.0 g sample of rubber compound is 85 percent natural rubber (cis-polyisoprene, units of 68 g/mol) by mass; the rest does not react with bromine. Assuming each adds one (Br = 80), the mass of bromine taken up is

  1. A18.8 g
  2. B32.0 g
  3. C8.0 g
  4. D16.0 g

Answer: D

Rubber mass = 0.85 x 8.0 = 6.8 g = 0.100 mol of repeat units, and each unit has one . Bromine = 0.100 mol x 160 g/mol = 16.0 g. Using the whole 8.0 g would give 18.8 g.
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