Liquid electrolytes ionize and hence a current can pass through them. So if a gas can ionize, can it conduct electricity too? If so, what are a few such gases?
Electric Conduction: At atmospheric pressure, air and other gases are poor conductors (Insulators) of electricity. 'Cause they don't have any free electrons to carry current. But, once free electrons are produced in gas by ionization (They become plasmas), discharge of electricity through gases appears. This could be done in many ways such as applying large potential difference across a gas column at very low pressure or by allowing high frequency EM-waves such as the X-Rays through the gas. This question is not proper to ask. Indeed, Gases become Plasmas once they're ionized..!
How? All Dielectrics have a certain value of breakdown potential - A potential which provides sufficient energy to break some covalent bonds and produce free electrons. These free electrons are accelerated by the applied electric field and they collide and ionize other atoms to produce more free electrons (Thus, they multiply by collision). This process is called Avalanche Breakdown. As there are large number of free electrons available for current flow
Examples: Discharge tubes, Lightning, etc.