Question 20

Question

How many half-lives does it take a radioactive substance to decay until only one-eighth of the original substance remains?

a
two
b
three
c
six
d
eight

Answer 1

To determine how many half-lives it takes for a radioactive substance to decay to one-eighth of its original amount, we can use the concept of half-lives.

1. After 1 half-life, 1/2 of the original substance remains.
2. After 2 half-lives, (1/2) × (1/2) = 1/4 of the original substance remains.
3. After 3 half-lives, (1/4) × (1/2) = 1/8 of the original substance remains.

Therefore, it takes three half-lives for a radioactive substance to decay to one-eighth of its original amount.

The correct answer is b) three.