Given an original sample of 100 g of an isotope with a half-life of 30 minutes, after one hour (equivalent to two half-lives), 25 g of the isotope will remain.
To determine how much of the isotope will be left after an hour, we need to consider the half-life of the isotope. The half-life is the time it takes for half of the original sample to decay.
Given that the half-life of the isotope is 30 minutes, we can calculate how many half-lives occur within an hour. Since there are 60 minutes in an hour, there are two half-lives in one hour (60 minutes divided by 30 minutes per half-life).
Each half-life reduces the amount of the isotope by half. Therefore, after the first half-life (30 minutes), half of the original sample will remain, which is 50 g (half of 100 g). After the second half-life (another 30 minutes), half of the remaining sample will remain, which is 25 g (half of 50 g).
So, after one hour, which is equivalent to two half-lives, 25 g of the isotope will be left.