The correct answer is option-1: To increase the life of the bulb.

When tungsten wire is heated to a high temperature, it emits visible light. However, at higher temperatures, tungsten wire tends to evaporate and degrade over time. This reduces the lifespan of the bulb.

Argon gas is used in an electric bulb to address this issue and increase the longevity of the bulb. The gas is inert, meaning it does not react easily with other chemicals. By filling the bulb with argon gas, it creates an environment that reduces the evaporation of the tungsten wire. This helps to maintain the integrity of the wire and prolong the lifespan of the bulb.

In addition to extending the lifespan of the bulb, the use of argon gas also helps to stabilize the emitted light. It prevents the tungsten wire from oxidizing and keeps the filament from deteriorating, thus reducing the risk of the bulb going out due to filament failure.

Therefore, argon gas is used with tungsten wire in an electric bulb to increase its lifespan and ensure a more stable and consistent light output.