For each of the following, indicate if the number of half-lives elapsed is:1. one half-life2. two half-lives3. three half-livesc. a sample of Au-198 with a half-life of 2.7 days after 5.4days

The half-life of iodine-131, an isotope used in thyroid therapy, is 8.021 days. What percentage of iodine-131 remains in a sample that is estimated to be 40.11 days old?

What is the concentration of a CO₂ in a container after 4 half-lives if 0.325 mol of CO2 is initially placed into a 5.0 L reaction vessel?

What is the half-life of the radioisotope that shows the following plot of remaining percentage vs. time?