Answer: Argon
This question has two parts, one concerning the atmosphere on Earth and one concerning the universe as a whole.
First question: What is the most abundant noble gas on Earth?
The answer undoubtedly is Argon.
Second Question: What is the most abundant noble gas in the universe?
The answer changes from the previous question to this one, in this case the answer is helium, not Argon. It may not make up much of Earth’s atmosphere, but there are places elsewhere in the universe where helium is incredibly abundant, that being stars. I am going to do a quick run down of how fusion in stars works:
In stars like the Sun, fusion, the forceful combination of two or more elements to make a larger element, occurs because of the incredible pressure that the inside of the Sun feels. The large pressure is caused by gravity and the massively large mass that the Sun has; this pressure is enough to force elements together. At the start, particularly when a star first starts out, it begins fusing all the excess hydrogen it has into helium, this is because a helium atom is simply two hydrogen nuclei. After a helium atom is made, it can then fuse with another helium atom to form beryllium, etc; this continues to happen until iron is formed.
Helium is also the second most abundant element in the universe because of the fact that it is created via fusion in stars. And also, as the elements get heavier and heavier, they become less and less abundant. Think about it like this: If you have 8 hydrogens to start out, fusion creates 4 heliums, then 2 Berylliums from those 4, then 1 Oxygen, and so on if given more hydrogens. As you go down the “fusion tree”, they become less and less abundant as you go on. And since stars are so common and huge, this explains why helium is the most abundant noble gas and hydrogen is the most abundant element in the universe.
Hope this makes sense to answer your question. I know I could make a simpler answer that is less comprehensive but where is the fun in that?
