We all know there is oxygen in air because we breathe it to live. However, the air around us is mostly nitrogen — about 78 percent. Nitrogen is fairly non-reactive and not poisonous. Also, it has no smell or taste, which is why we don't notice it.
About 20 percent of the air is oxygen, which is what we breathe, but it is flammable and highly reactive. Rust on iron and the bitter taste of old coffee are examples of oxygen reactions.
The third most plentiful gas is the non-reactive argon at 1 percent. The remaining 1 percent of our atmosphere is made up of many gasses including carbon dioxide, water vapor and a large number of other gasses in just trace amounts. Although it is a small part of the atmosphere by volume, it is water vapor that is the most important gas as far as weather is concerned.