Mean Life: The mean life (time constant) of radon-222 is 5.526 d. If a sample of radon initially contains 6.00 × 108 radon atoms, how many of them are left after 10.0 d?
A. 9.82 × 107
B. 7.67 × 107
C. 8.34 × 108
D. 7.29 × 108
E. 8.56 × 108
Answer: A
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