Decomposition of X exhibits a rate constant of 0.05 μg/year. How many year are required for the decomposition of 5 μg of X into 2.5 μg?

(1) 50
(2) 20
(3) 25
(4) 40

Correct answer: (1) 50

Solution

The rate constant has units ug/year, so the decomposition is zero order. Amount to decompose = 5 - 2.5 = 2.5 ug. Time = 2.5/0.05 = 50 years.

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