Question

A radioactive sample consist of two distinct spices having equal number of atoms intially. The mean life one spices is \(\tau\) and that ofother 5 \(\tau\) . The decay products in both cases are stable. The following figure shows graphs P, Q, R, S the plot of the total number of radioactive nuclei as a function of time. Which of the graphs P, Q, R and S represent the best form of the plot?

(1) P

(2) Q

(3) R

(4) S

Answer 1

(4) S

Since it is the process of radioactivity decay the total number of atoms cannot remains constant (as in option 1). Also the total number of atoms cannot ever increase (as in option 2 and 3). The total number of atoms can only decrease with time. Hence option (4) is the best plot.