Q. A radio-isotope has a half-life of $5\ years$. The fraction of the atoms of this material that would decay in $15\ years$ will be
A) 1/8
B) 2/3
C) 7/8
D) 5/8
Explanation
(c) $\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{15/5} = \frac{1}{8} \Rightarrow$ Decayed fraction $= 1 - \frac{1}{8} = \frac{7}{8}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.