Radioactive decay of which of the following isotopes in the Earth’s crust leads to generation of argon?

Answer: [A] K-40

Potassium-40, which is a rare radioactive isotope of potassium has a very long half life. It undergoes all three types of beta decay (β−, β+ and electron capture). About 89% of the time 40K decays to calcium-40 (40Ca). However, 11% of the time it decays to argon-40 (40Ar).

This question is a part of GKToday's Integrated IAS General Studies Module