Question

A sample of a radioisotope in a rock has decayed to 25 percent of its original radioactivity over a period of 12,000 years. the half-life of the radioisotope is

a. 3,000 years.
b. 4,000 years.
c. 6,000 years.
d. 8,000 years.
e. 10,000 years.

Answer 1

The correct half-life of the radioisotope that has decayed to 25% of its original activity over 12,000 years is 6,000 years.

Step-by-step explanation:

When considering the decay of a radioisotope in a rock from 100% to 25% of its original activity over 12,000 years, we can understand that this process involves two half-lives. After the first half-life, the remaining isotope activity would be 50%, and after the second half-life, it would be 25% of the initial activity. Therefore, since it took 12,000 years to undergo two half-lives, one half-life equals 6,000 years. So, the correct answer is c. 6,000 years.