A and B are two radioctive substance with half lives 20 min and d30 min respectively. Starting from equal number of moles A and B , after 1hr , what is the (a) ratio of moles of A and B and (b) ratio of activity of A and B ?

Explanation

The given time, `1` hour is `3t_(1//2)` for substance A and `2t_(1//2)` for substance B
The fraction of A left after `3t_(1//2)=1//2^(3)=1//8`
The fraction of B left after `2t_(1//2)=1//2^(2)=1//4`
(a) The ratio of moles left `=1//8 : 1//4=1 :2`.
(b) The ratio of activities =
`(lambda_(A)N_(A))/(lambda_(B)N_(B))=(N_(A)(t_(1//2))_(B))/(N_(B)(t_(1//2))_(A))=((1//8)xx30)/((1//4)xx20)=3 : 4`