Answer: After four half-lives, only 1/16 or 6.25% of the original parent isotopes remain.
Explanation:Here's how you can calculate it step by step:
1. Determine the half-life of the parent isotope. The half-life is the time it takes for half of the parent isotopes to decay into daughter isotopes.
2. Multiply the half-life by the number of half-lives to find the total time that has passed. In this case, since we are looking at four half-lives, multiply the half-life by 4.
3. Calculate the fraction of remaining parent isotopes using the formula: (1/2)^(number of half-lives). In this case, since we have four half-lives, the calculation is (1/2)^4.
4. Simplify the fraction to get the decimal representation. (1/2)^4 is equal to 1/16, which is equivalent to 0.0625 or 6.25% when expressed as a percentage.
Therefore, after four half-lives, only 1/16 or 6.25% of the original parent isotopes remain.