Not a constituent of air –
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).
H2
N2
O2
CO2