The correct option is A Argon
The closed glass chamber of the bulb contains an inactive (inert) gas, argon. The glass chamber can not be filled with air as the presence of oxygen will cause the filament to burn. The glass chamber can not be made vacuum. As in vacuum condition, the filament will evaporate because of very high temperature making the bulb unusable. The only solution to these problems is an inert gas. The inert gas within the bulb will maintain a particular pressure, preventing the filament from evaporating. An inert gas will not react with the filament. Nitrogen is also used like argon since it is unreactive.