The half-life of a radioactive isotope is 20.0 minutes. What is the total amount of a 1.00-gram sample of this isotope remaining after 1.00 hour? 0.500 g 0.333 g 0.250 g 0.125 g

## Step 1<br />The half-life of a radioactive isotope is the time it takes for half of the atoms in a sample to decay. In this case, the half-life of the isotope is given as 20.0 minutes.<br /><br />## Step 2<br />We need to find out how many half-lives have passed in 1.00 hour. Since 1 hour is 60 minutes, we divide 60 by 20 to get 3 half-lives.<br /><br />## Step 3<br />After each half-life, the amount of the isotope remaining is halved. So, after 1 half-life, 0.5 grams of the isotope remains. After 2 half-lives, 0.25 grams remain. After 3 half-lives, 0.125 grams remain.