This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and Health, Subject name: Social & Preventive Medicine
Maximum contribution to atomospheric air is- 
Select and explain. 
A. N2, B. O2, C. CO2, D. Helium
A: N2
Answer: A: N2 
Explanation: Ans. is 'a' i.e., N2 * The constituents of air:-# Major - Nitrogen (N2) - 78.1 %, Oxygen (O2) - 20.93%, Carbon dioxide (CO2) - 0.03%# Minor - Argon, neon, krypton, xenon, helium, water vapour, traces fo ammonia, suspended matter (dust, bacteria, spores, vegetable debris).