A first order reaction and a zero order reaction have the same initial concentration and the same half-life of $60 min$ . At $t = 90 min$ the ratio $[A]_{first} / [A]_{zero}$ is

Answer: C

First order:

[A] / [A]_{0} = (1/2)^{90/60} = 0.3536

. Zero order:

[A] / [A]_{0} = 1 - k t / [A]_{0} = 1 - 90/ (2 \times 60) = 0.25

, since

k = [A]_{0} / (2 t_{1/2})

. The ratio is

0.3536/0.25 = 1.41