Q. 99% of a radioactive element will decay between
A) 6 and 7 half lives
B) 7 and 8 half lives
C) 8 and 9 half lives
D) 9 half lives
Explanation
(a) $N = N_{0}\left( \frac{1}{2} \right)^{n} \Rightarrow \frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{n} \Rightarrow \frac{1}{100} - \left( \frac{1}{2} \right)^{n} \Rightarrow 2^{n} - 100$
$n$ comes out in between 6 and 7
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.