The half life period of a first order reaction is 10 min. The time required for the concentration of the reactant to change from 0.08M to 0.02M

Initial concentration, ${\mathrm{A}}_0=0.08 \mathrm{M}$

Half life period, ${\mathrm{t}}_{\frac{1}{2}}=10 \min$

To reduce the concentration of the reactant from 0.08 M to 0.02 M, time required is

0.08 $\to$0.04 10 min

0.04 $\to$0.02 10min

$\therefore$Total time, t =10 +10 =20min