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 co2.

Decomposition of sodium bicarbonate produces pure carbon dioxide and decomposition of hydrogen peroxide produces pure oxygen.
The amount of carbon dioxide in exhaled air is greater than that in regular air. Thus, the order is:

gas from decomposition of NaHCO₃ → Exhaled air → Air → gas from the decomposition of H₂O₂