Argon is the third most common gas in the Earth’s atmosphere, at 0.93%. This gas is generated due to decay of which among the following isotopes in the Earth’s crust ?

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 (ß-, ß+ 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