The half-life of a particular radioactive isotope of element X is 100 years.If you know that 500 years ago a fossil contained 10 mg of this isotope, you would expect to find about _______ mg in that fossil today.

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The half-life of the isotope is 100 years, meaning the amount of the isotope halves every 100 years. In 500 years, this process would occur 5 times (500 years / 100 years per half-life = 5 half-lives). Starting with 10 mg, after 5 half-lives, the amount would be halved 5 times: 10 mg → 5 mg → 2.5 mg → 1.25 mg → 0.625 mg → 0.3125 mg, which is approximately 0.3 mg.

The Half-Life of a Particular Radioactive Isotope of Element X