The gas which is filed in tungsten lamp is ________.

Explanation

**Step-by-Step Solution:**

1. **Identify the Type of Gas Used in Tungsten Lamps:**
- Tungsten lamps are commonly filled with an inert gas to prevent the filament from oxidizing and to prolong its life.

2. **Determine the Inert Gas Used:**
- The most commonly used inert gas in tungsten lamps is argon. Argon is a noble gas that does not react with tungsten or other materials in the lamp.

3. **Explain the Function of Argon in Tungsten Lamps:**
- Argon gas serves two main purposes:
- It prevents the tungsten filament from reacting with oxygen, which would lead to oxidation and a shorter lifespan of the filament.
- It slows down the evaporation of the tungsten filament, helping to maintain the integrity and performance of the lamp over time.

4. **Conclude with the Answer:**
- Therefore, the gas which is filled in tungsten lamps is **argon**.

**Final Answer:**
The gas which is filled in tungsten lamp is **argon**.

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