The radioactivity of a sample is R1 at a time T1 and R2 at a time T2 . If the half life of the specimen is T, the number of atoms that have disintegrated in the time (T2 –T1 ) is proportional to
(a) (R1 T1 – R2 T2)
(b) (R1 – R2)
(c) (R1 – R2)/T
(d) (R1 –R2) ×T
