A container holds 64 atoms of a radioactive isotope. This isotope has a half-life of 1.5 months. How many atoms of the radioactive isotope will be in the container after 3 months, or two half-lives.

16

Explanation:

Initial number of atoms, No = 64

Half life, T = 1.5 months

t = 3 months

number of half lives, n = t / T = 3 / 1.5 = 2

So, according to the radioactive law

After one half life, the number of atoms left = No / 2 = 64 / 2 = 32

After one more half life, the number of atoms left = 32 / 2 = 16