Question

Radon is a naturally occurring radioactive gas. It is on of the products produce as uranium decays. Radon has a half-life of approximately 4 days. If you have a sample of radon with a mass of 4 grams, how many grams will be left at the end of 8 days?

(A) 4

(B) 2

(C) 1

(D) none of these

Answer 1

d of course it would be none

Answer 2

Every 4 days, the amount of radon you started with is reduced by half.

Start with 4 grams of radon on day 1

After 4 days, you have (1/2)* 4 grams of radon = 2 grams

Start with 2 grams of radon on day 5

After four more days (end of day 8) you have:

(1/2)*2 grams = ?