A Rock Contains 0

question 36

Multiple Choice

A rock contains 0.37 mg of Pb-206 and 0.95 mg of U-238. Approximately how many U-238 atoms were in the rock when it was formed billions of years ago? (The half life for ²³⁸U → ²⁰⁶Pb is 4.51 × 10⁹ yr.)

• A) 1.32 atoms
• B) 5.8 × 10^-6 atoms
• C) 2.4 × 10¹⁸ atoms
• D) 3.3 × 10¹⁸ atoms
• E) 3.5 × 10²¹ atoms

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