Which of the following noble gases is present in the Earth's atmosphere in maximum percentage by volume?

Options

A. Argon
B. Radon
C. Helium
D. Xenon

Answer

1

Explanation

All the stable noble gases `(He, Ne, Ar, Kr and Xe)` are found in the atmosphere although onl argon is present in a high proporion (`0.93%` by moles ) .The high abundance of `Ar` in the atmosphere is a result of the radioactive decay of potassium `-40`, the naturally occurring radioactive isotope of `K`. This isotope has two decay pathways ,one of which involves the capture of a core electron to from argon-`40`:
`._(19)^(40)Krarr._(20)^(40)Ca+._(-1)^(0)e(89%)`
`._(19)^(40)K+._(-1)^(0)e rarr._(18)^(40)Ar(11%)`
Helium is found in high concentration in some underground natural gas deposits where it hasbeen accumulating from the decay of radioactive element in the Earth's crust.
All the other noble gases are obtained as by-products of the productions of dioxygen from air. Some `Ar` is also obtained from industrial `NH_(3)` synthesis (Haber process), where it accumlates during the recycling of the unused atmosphereic gases.