The half life of Po-218 is three minutes. How much of a 200 atom sample will remain after 15 minutes

6.25 atoms

Explanation:

We are given;

The half life of Po-218 is 3 minutes Initial sample is 200 atom Time of decay is 15 minutes

We are required to calculate the remaining mass after decay;

Half life refers to the time taken for original amount of a radioactive sample to decay to a half.

To calculate the remaining mass we use the formula;

N = N₀ * 0.5^n where n is the number of half lives, N is the new amount and N₀ is the original amount.

n = 15 min : 3 min

= 5

Therefore;

New amount = 200 atom * 0.5^5

= 6.25 atoms

Therefore; the amount of the sample that will remain after 15 minutes is 6.25 atoms.