Rank the four gases (air, exhaled air, gas produced from the decomposition of H2O2, gas from decomposition of NaHCO3) in order of decreasing concentration of oxygen).
air = 70 % N2
exhaled air =70%N2 + some less O2 compared to only air
2H2O2=2H2O+O2
NaHCO3=2NaHCO3 → Na2CO3 + H2O + CO2 = No O2 gas from decomposition
ssoooo NaHCO3 <exhaled air <air <H2O2