The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to ( 116 )th of its initial value?
- 40 minutes
- 60 minutes
- 80 minutes
- 20 minutes
Answer
(3) 80 minutes
Solution
AA0 = ( 12 )n = 116
n = 4 half-lives
t = n T1/2 = 4 20 = 80 minutes
Answer: (3)