We can find out more about them by testing them. Gasses react in different ways to a burning or glowing splint. First the gas has to be generated and trapped. Alka Seltzer and water together release carbon dioxide. When a burning splint is placed in carbon dioxide it promptly goes out.
Carbon dioxide is used in some fire extinguishers.
To generate oxygen, add 5 ml of hydrogen peroxide to a pinch of yeast or manganese dioxide. To test oxygen, a glowing splint placed in it will burst back into flame. The oxygen itself is not burning but it supports combustion. If you want to try a third gas, hydrogen, it burns very quickly and makes a popping sound in the test tube. It can be generated by mixing a weak hydrochloric acid solution with magnesium or zinc.