We can prove by the following experiment that CO2 is present in the exhaled air:
Experiment. Set up the apparatus as shown in the figure. Exhale air through your mouth into the tube provided for this purpose. You will notice that the lime water is kept in test B. Through which exhaled air is passing has turned milky.
On the other hand, test tube A through which exhaled air is not passing has shown slight milkiness due to atmosphere air entering from the side tube. It proves that carbon dioxide is present in exhaled air which has turned lime water present in test tube B milky and milkiness is due to the formation of calcium carbonate in the figure.
