Question

How much of the parent isotope would be remaining after 7 half-lives have passed?

A. 6.25%
B. 1.56%
C. 0.78%
D. 0.39%

Answer 1

After 7 half-lives, the remaining amount of a parent isotope would be 0.78%, which means that answer C is the correct one.

Step-by-step explanation:

The student's question about the remaining amount of a parent isotope after 7 half-lives can be answered using the concept of half-life in radioactive decay. The initial amount of the parent isotope is halved with each half-life that passes. So, after 7 half-lives, the amount of parent isotope remaining can be calculated as: \( \frac{1}{2^7} \) or \( \frac{1}{128} \). To find the percentage, this fraction is converted into a percentage as follows: \( \frac{1}{128} \times 100\% = 0.78125\% \), which can be rounded to 0.78%. Therefore, the correct answer is C. 0.78%.