Question

Scientists have found that the Uranium-235 content of an unknown prehistoric sample was reduced to one-fourth. What best describes the identity of the sample?

Answer 1

Answer:

Half-Life is the time for a substance (U-235 in this case) to decay to 1/2 its original mass.

Since the problem is asking for the time for U-235 to decay to 1/2 its original mass (100 grams to 50 grams) then the decay time is 1 half-life, or 700 million years.

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