Q. Radon $(Rn)$ decays into Polonium $(Po)$ by emitting an $\alpha -$particle with half-life of 4 days. A sample contains $6.4 \times 10^{10}$ atoms of $Rn$. After 12 days, the number of atoms of $Rn$ left in the sample will be
A) $3.2 \times 10^{10}$
B) $0.53 \times 10^{10}$
C) $2.1 \times 10^{10}$
D) $0.8 \times 10^{10}$
Explanation
(d) In the given case, 12 days = 3 half lives Number of atoms left after 3 half live
$= 6.4 \times 10^{10} \times \frac{1}{2^{3}} = 0.8 \times 10^{10}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.