Which gas is least abundant in earth's atmosphere?

Answer 1

After you get rid of the big players like nitrogen (78%), oxygen (21%), and argon (1%) the remaining gases are very rarified. The standard list runs from helium(0.0005%) down to xenon at 0.000008%. There are gases mor are than xenon but they are usually not mentioned.

Answer 2

Ozone is the least abundant gas in Earth's atmosphere. It makes up a very small fraction of the atmosphere, primarily found in the stratosphere.