Question

why is argon gases usen in light bulbs?

Answer 1

In light bulbs the tungsten filament is subjected to high temperature, therefore  a gas present in the bulb may react with the filament unless it is a noble gas....argon being the most abundant noble gas is thus preferred over other noble gases.

Answer 2

since argon is a noble gas so it helps to react with the filament of the bulb so it is used in the bulbs