Q. What percentage of original radioactive atoms is left after five half lives
A) 0.3%
B) 1%
C) 31%
D) 3.125%
Explanation
(d) Fraction of atoms remains after five half lives
$\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{t/T} = \left( \frac{1}{2} \right)^{5T/T} = \frac{1}{32}$
$\Rightarrow$ Percentage atom remains $= \frac{1}{32} \times 100 = 3.125\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.