A 60-g sample of radioactive isotope is measured after two half-lives have passed. What pair of percentages describes the sample after two half-lives? 50% unchanged and 50% stable 25% unchanged and 75% stable 12.5% unchanged and 87.5% stable 75% unchanged and 25% stable

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Houston West

9 September, 01:19

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Renee Bryant · Answer 1

60 grams

1) 60 grams x 1/2 = 30 grams

2) 30 grams x 1/2 = 15 grams

15/60 = 0.25% unchanged

I think the answer is 25% unchanged and 75% stable