This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Not a constituent of air – 
Select and explain. 
A. H2, B. N2, C. O2, D. CO2
A: H2
Answer: A: H2 
Explanation: Air 

The immediate environment of man comprises of air on which depends all forms of life.
The requirement for air is about 10-20 M3/day.
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).