Q. A radioactive element A decays into B with a half-life of 2 days. A fresh prepared sample of A has a mass of 12 g. What mass of A and B are there in the sample after 4 days?
A) $A = 3g\ ,\ B = 9g$
B) $A = 6$g , $B =$6g
C) $A =$12g , $B =$0g
D) $A =$9g , $B =$3g
Explanation
(a) After 2 days , we have
$A = 6g,\ B = (12 - 6)\ g = \ 6g$
After 4 days, we have
$A = 3g,\ B = (12 - 3)\ g = \ 9g$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.