We talk about the air as though it were just one gas, but it is actually a mixture of many gases.
We all know we need air to breathe, but we use just one of the gases in the air – oxygen – for our breathing. Oxygen makes up about a fifth of the air.
Nearly all of the rest is nitrogen. It does no harm, but we can't use it either. All other gases, like moisture, are present in tiny amounts.
