Neon, Argon, Natural, Methane and Helium. Or other ones are : Oxygen, Hydrogen or Carbon Dioxide.
Freon is a gas often used in refrigeration or cooling process.
OxygenNitrogenArgonHydrogenCarbon di oxideBiogasAcytyleneKrypton, Neon and XenonOzone
Well i really do no the answer to this question it is well okay you caught me i dont no but i think it might be like pi.