Which one of the following gases, present in the air near the surface of the Earth, has maximum concentration?

The Earth's atmosphere is a complex mixture of gases where nitrogen (N2) is the most abundant constituent. Near the Earth's surface, dry air is composed of approximately 78.08% nitrogen by volume [c1][c2]. Oxygen (O2) is the second most prevalent gas, accounting for about 20.95% [t1][t4]. Other gases exist in much smaller concentrations: argon makes up about 0.93%, while carbon dioxide, methane (CH4), and hydrogen (H2) are considered trace gases [c1][t2]. Specifically, methane has a concentration of approximately 0.000179% and hydrogen is even lower at 0.00005% [c2]. Because heavier gases like nitrogen and oxygen tend to remain concentrated in the lower layers of the atmosphere (the troposphere), nitrogen consistently maintains the maximum concentration near the surface [c2][t1].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > 20.1. Composition of The Earth's Atmosphere > p. 270
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Permanent Gases of The Atmosphere > p. 271
3. [3] https://dspmuranchi.ac.in/pdf/Blog/Climatology_2_Final_.pdf
4. [4] https://www.sciencedirect.com/topics/physics-and-astronomy/earth-atmosphere