Question
Question: Half-lives of two radioactive substances A and B are respectively 20 min. and 40 min. Initially, the...
Half-lives of two radioactive substances A and B are respectively 20 min. and 40 min. Initially, the samples of A and B have equal number of nuclei. After 80 min. the ratio of the remaining numbers of A and B nuclei is-
A
1 : 16
B
4 : 1
C
1 : 4
D
1 : 1
Answer
1 : 4
Explanation
Solution
Use, N = N0/2n Ž NA = 280/20N0=24N0
NB= 280/40N0=22N0 Ž NBNA=41
Ž NA : NB :: 1:4