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. `7.5` minutes
B. `15` minutes
C. `30` minutes
D. `60` minutes

Answer

C

Explanation

The concentration of the reactants decrease from `0.8` to `0.4` in `15 min` i.e., `T_(1//2) = 15 min`, concentration from `0.1 m` to `0.025` will fall in `2` half lives so total time taken `= 2 xx T_(1//2) = 2 xx 15 = 30 min`.