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 `3 t_(1//2) = //2^(3) = 1//8`
The fraction of A left after `3 t_(1//2) = 1//2^(3) = 1//8`
(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`