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
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Discussions (5)
Given that a whole mass of elements A and B exists respectively (note: 1 stands for a whole), then:
For element A, after 100 years, we have A of mass 1/2 remaining
After 200 years, we have the mass of A reduced by half again; i.e 1/2 becomes 1/4
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For element B, after 50 years, we have B of mass 1/2 remaining
After 100 years, we have the mass of B reduced by half again; i.e 1/2 becomes 1/4
After 150 years, we have the mass of A reduced by half again; i.e 1/4 becomes 1/8
After 200 years,we finally have the mass of A reduced by half again; i.e 1/8 becomes 1/16
Ratio of A:B after 200 years....
A is 1/4 while B is 1/16
=1/4 : 1/16
= 1/4 ÷ 1/16
= 1/4 × 16/1
= 4/1
= 4:1 (option A ✓)
PLease explain it vividly,because i dont understand how u arrived at the answer.
