Question

A radioactive sample starts with 800,000 undecayed nuclei. After 12 hours, 700,000 of the nuclei have decayed. What is the half-life of the sample?

A. 3 hours

B. 12 hours

C. 6 hours

D. 4 hours

Answer 1

100,000 / 800,000 = 1 / 8 amount of sample after 12 hours

(1/2)^n = 1 / 8 after n half-lives 1/8 of sample will be left

n = 3

(D) is the correct answer - 1/2 half-life = 4 hours