After `280` days, the activity of a radioactive sample is `6000` dps. The activity reduces to `3000` dps after another `140` days. The initial activity of the sample in dps is

Options

A. `6000`
B. `9000`
C. `3000`
D. `24000`

Answer

D

Explanation

Activity reduces from `6000` dps to `3000` dps in 140 days. It implies that half-life of the radioactive sample is `140` days. In `280` days for two half-lives) activity ill remain `1/4` th of the initial activity. Hence the initial activityof the sample is `4xx6000 dps=24000dps`