5g would remain
I suppose that you think to the radioactive isotope Cs-17; After 4 years remain 9,122 g.
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
As you did not specify an isotope of cesium, I will assume you meant natural cesium. Natural cesium is not radioactive so it does not decay. There will always be the same 10 g of cesium, no matter how long you wait.
I suppose that you think to the radioactive isotope Cs-17; After 4 years remain 9,122 g.
2 1/2 g
2 1/2 g
2 1/2 g
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.
1 1/4 g (apex)or 1.25 g
11/4 g apex
2 1/2g
As you did not specify an isotope of cesium, I will assume you meant natural cesium. Natural cesium is not radioactive so it does not decay. There will always be the same 10 g of cesium, no matter how long you wait.
Since the half-life of cesium-137 is about 30 years, 3 half-lives would have passed in 90 years. The first half-life would leave .5 mg of cesium-137. The second would leave .25 mg, and the third half-life would leave .175 mg of cesium-137.