Uranium-238 decays to lead-206 with a half-life of 4.5 x 109 yr. determine how much uranium-238 decays in milligrams (to three significant figures) if a 4.60 mg sample of uranium-238 decays for 4.1 x 109 yr.

2.15 mg of uranium-238 decays

Explanation:

For decay of radioactive nuclide-

where N is amount of radioactive nuclide after t time, is initial amount of radioactive nuclide and is half life of radioactive nuclide

Here , and

So,

so, N = 2.446 mg

mass of uranium-238 decays = (4.60-2.446) mg = 2.15 mg

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