A fraction f1 of a radioactive sample decays in one mean life, and a fraction f2 decays in one half-life
Answer & explanation
Correct answer: option 1
$T_{mean} = 1.44 \times T_{\frac{1}{2}}$
$\text{So the time span of 1 mean-life is more than that of 1 half-life.}$
$\text{Thus, number (and fraction) of radioactive sample decay would be more in 1 mean-life than that in 1 half-life.}$
$\Rightarrow f_1 > f_2$