A radioactive sampleconsists of two distinct species having equal number of atoms initially. The mean life time of one species is t and that of the other is 5t. 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 figures best represents the form of this plot[IIT-JEE (Screening) 2001]

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