Optically pure (R)-X racemises in solution. The enantiomeric excess falls by a first-order process with rate constant $0.0462 h^{- 1}$ . The time needed for the ee to fall from 100% to 25% is

Answer: D

For first-order decay ee

_{t}

= ee

_{0} e^{- k t}

, so

t = ln (100/25) / k = ln 4/0.0462 = 30.0

h. 15.0 h is the half-life (

ln 2/ k

), which would give 50% ee, and 60 h would give 6.25% ee.