6.25 atoms
We are given;
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.
