Original: A pure gas may be made up of individual atoms ( e.g. a noble gas or atomic gas like neon ) , elemental molecules made from one type of atom ( e.g. oxygen ) , or compound molecules made from a variety of atoms ( e.g. carbon dioxide ) .
Simplified: An example of a pure gas is Neon , an example of an elemental gas is Hydrogen and an example of a compound gas could be Carbon Dioxide .