A radioactive sample consists of two distinct species having equal number of atoms initially. The mean life of one species is `tau` and that of the other is `5 tau`. The decay products in both cases are stable. A plot is made of the total number of radioactive nuclei as a function of time. Which of the following figure best represents the form of this plot?
(a), (b), (c), (d)

Answer

D

Explanation

The total number of atoms can neither remain constant ( as in option a) nor can ever increase (as in options b and c). They will continuously decrease with time. Therefore, (d) is the appropriate option.