Final answer:
Argon is the most abundant noble gas in Earth's atmosphere, significantly exceeding the concentrations of other noble gases like helium and neon.
Step-by-step explanation:
The most abundant noble gas in the atmosphere is argon (Ar). Despite noble gases being minor constituents of the Earth's atmosphere, argon stands out due to its significant volume concentration compared to other noble gases. Noble gases like helium, neon, argon, krypton, xenon, and radon are monatomic and exhibit very low reactivity due to their full valence electron shells. Therefore, these gases were historically referred to as inert or rare gases. Helium, for instance, is substantially present in natural gas, and argon's low reactivity makes it ideal for use in an inert atmosphere for welding and within light bulbs. Neon is known for its iconic red light in gas discharge tubes used in neon signs.