Which one of the following gases is placed second in respect of abundance in the Earth’s atmosphere ?

The Earth's atmosphere is primarily composed of a mixture of gases, with nitrogen and oxygen being the major components. Nitrogen (N2) is the most abundant gas, accounting for approximately 78.08% of the atmosphere's volume [3]. Oxygen (O2) is the second most abundant gas, making up about 20.95% (roughly 21%) of the dry air volume [3]. Following these two, argon is the third most abundant at approximately 0.93%, while carbon dioxide is a trace gas with a concentration of about 0.036% to 0.04% [2]. Hydrogen is present only in minute trace amounts, approximately 0.00005% [2]. Therefore, oxygen is the gas placed second in respect of abundance in the Earth's atmosphere, following nitrogen.

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] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > atmosphErE. > p. 6