Upon irradiating californium with neutrons, a scientist discovered a new nuclide having mass number of 250 and a half-life of 30 min. After 90 min. of irradiation, the observed radioactivity due to nuclied was 100 dis/min. How many atoms of the nucliede were prepared intially?
A. `2.4xx10^(4)`
B. `3.46xx10^(4)`
C. 1900
D. 800