Two radioactive elements A and B have half-lives of 100 a...
Two radioactive elements A and B have half-lives of 100 and 50 years respectively. Samples of A and B initially contain equal amounts/number of atoms. What is the ratio of the number of the remaining atoms of A to that of B after 200 years?
4 : 1
2 : 1
1 : 1
1 : 2
1 : 4
Correct answer is A
Given that a mass N of elements A and B exists, then:
For element A, after 100 years, we have A of mass N/2 remaining
After 200 years, we have A of mass 12×N2 = N4
For element B, after 50 years, we have B of mass N/2 remaining
After 100 years, we have B of mass 12×N2 = N4
After 150 years, we have B of mass 12×N4 = N8
After 200 years,we have B of mass 12×N8 = N16
Ratio: (N4:N16)
=4:16 = 1:4
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