Question

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

Answer 1

Answer: (A)

6 and 7 half lives

Answer 2

$N = N_{0}\left( \frac{1}{2} \right)^{n} \Rightarrow \frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{n} \Rightarrow \frac{1}{100} = \left( \frac{1}{2} \right)^{n} \Rightarrow 2^{n} = 100$

n comes out in between 6 and 7.