7. What do we breathe out?

This can be proved by a small activity:

 

 

 

The lime water in the second tube turns milky white.

 

We know that we inhale a mixture of gases. But from this activity we can say that we exhale carbon diode. This is because the lime water present in the second tube turns milky after a few seconds due to the presence of carbon dioxide in the air that we exhale. Hence we can say that carbon dioxide is present in the air that we exhale.