Concept:Oxidation of the hot filament is prevented by filling the bulb with an inert gas like argon.
Explanation:Oxidation requires oxygen, so the air inside the bulb must be removed.
The tungsten filament becomes extremely hot when current passes through it.
If oxygen is present, it reacts with the hot tungsten and the filament burns out quickly.
Argon is an inert gas, meaning it does not react with the filament.
Filling the bulb with argon displaces the air and prevents oxidation.
Argon also allows the filament to glow safely at high temperature.
Hydrogen is not used because it is flammable and reactive.
Oxygen would directly cause oxidation of the filament.
Mercury vapour is not suitable for this purpose in ordinary bulbs.
Answer:C. argon