A radioactive isotope has a half-life of 10 years. After 30 years, what fraction remains?

A) 1/2

B) 1/4

C) 1/8

D) 1/16

Explanation

After n half-lives, fraction remaining = (1/2)^n. 30/10 = 3 half-lives → (1/2)^3 = 1/8.