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The main constituents of atmospheric air are Oxygen (O2) and Nitrogen (N2). The composition of O2 and N2 is approximately :
Explanation
The Earth's atmosphere is composed of a mixture of various gases. According to standard scientific data and NCERT textbooks, Nitrogen (N2) is the most abundant gas, accounting for approximately 78.08% of the dry atmosphere by volume. Oxygen (O2) is the second most abundant gas, comprising about 20.95% (commonly rounded to 21%).
Together, these two primary constituents make up roughly 99% of the atmosphere. The remaining 1% consists of Argon (≈0.93%), Carbon Dioxide (≈0.04%), and trace amounts of other gases like Neon, Helium, and Methane. Based on these standard values, the approximate composition of 21% Oxygen and 78% Nitrogen matches Option C.