JAMB - Chemistry (2021 - No. 23)

The most abundant naturally occurring gas is Nitrogen (N2), which makes up about 78% of air. Oxygen (O2) is the second most abundant gas at about 21%. The inert gas Argon (Ar) is the third most abundant gas. 

Argon is the most abundant rare gas in the atmosphere. It is represented by the symbol Ar. The atomic number of Ar is 18.