(Solution) - Radon 222 is created in a series of radioactive decays starting -(2025 Original AI-Free Solution)

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Radon-222 is created in a series of radioactive decays starting with 23892U and ending with 20682Pb. The half-life of 222Rn is 3.8 days.
(a) If the half-life is so short, why hasn't all the 222Rn gas decayed by now?
(b) If the half-life of 222Rn were much shorter, say a few seconds, would it be more dangerous to us or less dangerous? What if the half-life were much longer, say thousands of years?