A Rock Sample from the Moon Includes a Mineral That

Multiple Choice

A rock sample from the moon includes a mineral that contains small amounts of the radioactive isotope Potassium- 40 and its daughter element Argon- 40 (half- life of 1.3 billion years) . This mineral would not form with any Argon- 40. Consider a crystal with 7 atoms of Argon- 40 for every 1 atom of Potassium- 40. How many atoms of Potassium- 40 were present when the crystal formed for each atom of Potassium- 40 that exists today?

A) 1
B) 7
C) 8
D) None