Ao = At x
2n                Â
- equation 1
Where,
          Â
Ao = Initial
amount                               Â
= 4.0 mg (given)
          Â
At = Amount remaining at time
t          =
?     Â
          Â
n = number of half-lives
Number of half-lives, n = total time elapsed /
half-life period = 5.0 years / 2.5 years = 2
Putting the values in equation 1-
4.0 mg = At x 22
Or, At = 4.0 mg / 4 = 1.0 mg
Hence, the amount of Q-234 remaining after 5.0 years =
1.0 mg
