The Radioisotope Potassium-40 Decays to Argon-40 by Positron Emission with a Half-Life

question 124

Multiple Choice

The radioisotope potassium-40 decays to argon-40 by positron emission with a half-life of 1.3 × 10⁹ yr.A sample of moon rock was found to contain 78 argon-40 atoms for every 22 potassium-40 atoms.The age of the rock is

• A)8.1 × 10^-10 yr
• B)2.4 × 10⁹ yr
• C)2.8 × 10⁹ yr
• D)4.6 × 10⁹ yr
• E)6.8 × 10⁹ yr

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