Electric bulbs (fill gas): Identify the gas usually filled in incandescent electric bulbs to protect the filament. Consider inertness and prevention of filament oxidation at working temperature. Choose the correct gas.

Given data

• Ask: Gas used inside incandescent bulbs.

Concept/Approach
Incandescent bulbs are filled with inert/neutral gases (commonly nitrogen, often mixed with argon) to prevent tungsten oxidation and to reduce filament evaporation.

Common pitfalls
Oxygen would quickly oxidize the filament; hydrogen/CO₂ are not used for this purpose.

Final Answer
Nitrogen