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JEE Advanced levelSingle correct optionDifficulty 3 of 3g3207

Reactant A gives P1 and P2 by parallel first-order steps with and . Each product can also revert to A, and at equilibrium . The product distribution early in the reaction and at equilibrium respectively is

  1. A80% P2 initially; 90% P1 at equilibrium
  2. B80% P1 initially; 90% P2 at equilibrium
  3. C50% each initially; 90% P2 at equilibrium
  4. D80% P1 initially; 90% P1 at equilibrium

Answer: B

Early on, reversal is negligible, so , i.e. 80% P1 (kinetic). At equilibrium the ratio is set by : P2 fraction (thermodynamic).
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