Explanation:

- Option 1: Argon

- Argon is an inert gas, which means it does not react readily with other substances.

- It is commonly used in light bulbs to prevent the tungsten filament from oxidizing.

- It forms a buffer between the filament and the outside environment, extending the bulb's lifespan.

- ?? Correct Answer!

- Option 2: Hydrogen

- Hydrogen is a reactive gas, not typically used in light bulbs.

- It is not inert and would not help in prolonging the bulb's life.

- Option 3: Oxygen

- Oxygen is highly reactive and would cause the filament to burn out quickly.

- Not suitable for use in light bulbs as an inert gas.

- Option 4: Radon

- Radon is an inert gas but is radioactive and rare.

- It is not used in light bulbs due to its radioactivity and scarcity.