Question

Half-lives of two radioactive elements A and B are 20 min and 40 min, respectively. Initially, the samples have equal number of nuclei.

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Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively.Initially, the samples have equal number of nuclei. After 80 minutes, the ratio of decayed numbers of A and B nuclei will be:

(1)1:16(2)4:1(3)1:4(4)5:4(1)1:16(2)4:1(3)1:4(4)5:4



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Solution :

80 minutes = 4 half-lives of A = 2 half-lives of B

Let the initial number of nuclei in each sample be N

NANA after 80 minutes =N24=N24

=> Number of A nuclides decayed =1516=1516NN

NBNB after 80 minutes =N24=N24

=> Number of B nuclides decayed =34=34NN

Required ratio =15/163/4=15/163/4

=54