Inert gases protect bulb filaments from oxidation

Steps:

• Determine bulb type: Incandescent bulbs use inert gases to prevent tungsten filament burnout.
• Recall standard gases: Argon (1) and nitrogen (3) are commonly mixed to reduce evaporation and extend life.
• Eliminate incorrect options: Helium or neon (2) are not typically used in standard incandescent bulbs.
• Match to choices: Correct combination is argon and nitrogen, excluding the third gas.

Why C is correct:

• Argon and nitrogen (1 and 3) form the standard inert gas mixture, as per bulb manufacturing standards, minimizing filament reaction with trace oxygen.

Why the others are wrong:

• A omits nitrogen, which is essential for thermal stability.
• B includes an incorrect gas like helium, unsuitable due to high thermal conductivity.
• D adds the wrong gas, overcomplicating the inert fill without benefit.

Final answer: C