The correct option is 1 only
Explanation
The atmosphere is a mixture of various gases, water vapour, and dust particles. The composition of clean, dry air is relatively constant in the lower atmosphere, dominated by two major gases that account for the vast majority of its volume.
Statement-wise Analysis
- Pair 1 is correctly matched: Nitrogen and Oxygen are the two primary components of the atmosphere. Nitrogen constitutes approximately 78% and Oxygen constitutes approximately 21% of the total volume. Together, they account for about 99% of the air.
- Pair 2 is incorrectly matched: Carbon Dioxide constitutes a very small fraction of the atmosphere, approximately 0.03% to 0.04%. The figure of 21% corresponds to Oxygen.
- Pair 3 is incorrectly matched: "Other gases" typically include Argon (0.93%) and trace gases like Neon, Helium, and Methane. The figure of 78% corresponds to Nitrogen, not the minor gases.
- Pair 4 is incorrectly matched: Water vapour is a variable component of the atmosphere. Its concentration varies geographically and climatically, ranging from nearly 0% in arid or cold regions to about 4% in warm, humid tropics. It never constitutes 50% of the air volume.
Key Takeaway
Composition of Atmosphere (by volume): Nitrogen (78.08%) > Oxygen (20.95%) > Argon (0.93%) > Carbon Dioxide (0.036%). Water vapour is highly variable (0–4%).