Question

a sample contains 36g of a radioactive isotope. how much radioactive isotope remains in the sample after 3 half-lives

Answer 1

After 1st half life it will be 36/2 i.e. 18gm then 9 gm and then 4.5 grams simply
Hope this is what you were searching for!

Answer 2

4.5 g

Step-by-step explanation:

N0 = 36 g, Let half life is T.

t = 3 T, n is number of half lives = t / T = 3

By using the decay law of radioactivity

N / N0 = (1 / 2)^n

where, N0 be the initial amount

N be the amount left

n be the number of half lives

N / 36 = (1/2)^3

N / 36 = 1 / 8

N = 36 / 8 = 4.5 g