Question

Analysis of potassium and argon atoms in a moon rock sample by a mass spectrometer shows that the ratio of the number of stable $$Ar^{40}$$ atoms present to the number of radioactive $$K^{40}$$ atoms is $$7:1$$. Assume that all the argon atoms were produced by the decay of potassium atoms, with a half-life of $$1.25\times 10^9$$ years. How old is the rock?

Answer 1

Correct option is B. $$3.75\times 10^9$$ year