Final answer:
Argon (C) is the odorless, colorless, unreactive gas used in most incandescent light bulbs.
Step-by-step explanation:
The odorless, colorless, unreactive gas used in most incandescent light bulbs is argon (C).
Argon is a member of the noble gas family, also known as group 18, which includes helium, neon, argon, krypton, xenon, and radon.
Noble gases are unreactive at room temperature and pressure, making argon an ideal choice for creating an inert atmosphere in light bulbs.
When argon is used in gas-filled electric light bulbs, its lower heat conductivity and chemical inertness inhibit the vaporization of the tungsten filament, prolonging the bulb's life.