Argon
Ar
The symbol for Argon is Ar. The atomic number is 18 and the mass number is 39.948. Argon is in period 3 and group number 18. Argon's in the noble gas group and is a non-metal.
Florescent lightbulbs
Used to fill them to prevent oxygen from corroding the hit filament.
Welding
Use it because it is a non-reactive so it is a good element when using really really high temp.
Vacuum tubes
Radios used to be much larger than they are now and had big glass tubes inside. The radio tubes were filled with argon gas.