A uranium-235 sample starts with 200 atoms, and 700 million years later, there are 100 atoms. What is the half-life of uranium-235?A.350 million yearsB.700 million yearsC.235 yearsD.100 year
Question
A uranium-235 sample starts with 200 atoms, and 700 million years later, there are 100 atoms. What is the half-life of uranium-235?A.350 million yearsB.700 million yearsC.235 yearsD.100 year
Solution
The half-life of a substance is the time it takes for half of the substance to decay. In this case, the uranium-235 sample started with 200 atoms and after 700 million years, there were 100 atoms left. This means that in 700 million years, the sample went through one half-life (as it halved from 200 atoms to 100 atoms). Therefore, the half-life of uranium-235 is 700 million years. So, the correct answer is B.700 million years.
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