The rate of a f irst -order react ion is
0.04 mol ``l^{-1} s^{-1}`` at 10 seconds and
0.03 mol ``l^{-1} s^{-1}``at 20 seconds after initiation of the
reaction. The half-life period of the reaction is :
(1) 24.1 s
(2) 34.1 s
(3) 44.1 s
(4) 54.1 s