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 d p s ) is

Step-by-step solution

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 (or two half-lives)activity will remain 1 4 th of the initial activity . Hence the initial activity of the sample is 4 × 6000 dps = 24000 dps