The correct conclusion to infer from a 3.0 picogram (pg) sample of curium-245 with a half-life of 8500 years is:
After 8500 years, the curium-245 sample is anticipated to possess a mass of roughly 1.5 picograms.
This is because, after one half-life (8500 years), half of the original sample will have decayed. If the sample starts at 3.0 pg, after 8500 years, it will decay to about 1.5 pg.