In a first order reaction, the concentration of the reactant decreases form `0.8 M` to `0.4 M` in `15 min`. The time taken for the concentration to change form `0.1 M` to `0.025 M` is

Options

A. `60 min`
B. `15 min`
C. `7.5 min`
D. `30 min`

Answer

D

Explanation

`0.8 M overset(t_(1//2) = 15 min)rarr0.4 M`
`:. 0.1 M underset(t_(1//2) = 15 min)rarr 0.05 M underset(t_(1//2) = 15 min)rarr 0.025 M`
Thus, total time `= (15+5) = 30 min`