A first-order reaction completes 75% in 30 minutes. Its half-life (using $t_{1/2}$ being independent of concentration for first order) is approximately:
A60 min
B7.5 min
C20 min
D15 min
Answer & Solution
Correct answer: D. 15 min
75% completion = two half-lives (50% → 75%). So $2 t_{1/2} = 30$ min ⇒ $t_{1/2} = 15$ min. (For first-order kinetics, $t_{1/2}$ is independent of starting concentration.)
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