Final answer:
After 1 hour, half of the original 80 grams of bismuth would remain (40 grams). Following another hour, another half would decay, leaving 20 grams, which corresponds to option a) 20 grams.
Step-by-step explanation:
The half-life of a radioactive substance is the time it takes for half of the radioactive nuclei to decay. Given that the half-life of a specific kind of bismuth is 1 hour, we can calculate the amount of bismuth left after successive half-lives.
If you start with 80 grams of radioactive bismuth, after 1 hour (one half-life), you would have half of this amount left, which is 40 grams. After another hour (two half-lives in total), half of the remaining 40 grams would decay, leaving you with 20 grams.
Therefore, after 2 hours, you would have 20 grams of the radioactive bismuth remaining, which corresponds to option a) 20 grams.