You must know the half life of Caesium to calculate this.
5g would remain
I suppose that you think to the radioactive isotope Cs-17; After 4 years remain 9,122 g.
Plutonium-239 has a half-life of about 24,100 years, meaning it takes that long for half of a sample to decay. In 43 years, which is much shorter than the half-life, only a tiny fraction of the plutonium would decay. Therefore, after 43 years, approximately 99.83 grams of the original 100-gram sample would remain.
The half-life of cesium-137 is approximately 30.1 years, not 2 years. After one half-life, 5 G of the original 10 G sample would remain. After two half-lives (about 60.2 years), 2.5 G would remain, and so on. If you meant a hypothetical isotope with a 2-year half-life, after 2 years, 5 G would remain, and after 4 years, 2.5 G would remain.
2 1/2 g
2 1/2 g
2 1/2 g
This would depend on the specific sample and its stability. Without additional information, it is not possible to determine how much of the sample would remain unchanged after two hours.
Approximately 400 grams of the potassium-40 sample will remain after 3.91 years, as potassium-40 has a half-life of around 1.25 billion years. This means that half of the initial sample would have decayed by that time.
2 1/2 g
2 1/2 g
After 6 years, approximately 5 grams of cesium-137 would remain from a 10 g sample due to its half-life of around 30 years. This decay is exponential, with about half of the original sample decaying every 30 years.