Above is a very simplified diagram of the composition (volume ratio) of inhaled and exhaled air. The process of breathing (respiration) is the exchange of gases in the body, where oxygen is breathed in and used, following by carbon dioxide being removed as a product of oxidation reactions. There is, therefore, a higher proportion of oxygen in the inhaled air than in the exhaled air and vice versa holds for carbon dioxide.
The proportion of carbon dioxide in exhaled air is approximately 100 times higher than in inhaled air. However, although the proportion of CO2 in the exhaled air increases this much, its proportion is still approximately three times lower than that of oxygen in the exhaled air. This is due to the fact that the proportion of CO2 in the inhaled air is extremely low (we are, therefore, in fact still breathing out a higher volume of oxygen than carbon dioxide).
Nitrogen (N) is the most abundant (almost 80 %) element in the Earth atmosphere (and thus also in the inhaled and exhaled air). It is a colorless and odorless gas, which is not dangerous (however some compounds containing N can be toxic, for example nitrogen oxides).