In colour discharge tubes,which is used?

Options

A. Ne
B. Ar
C. Kr
D. He

Answer

**Step-by-Step Solution:**

1. **Understanding Color Discharge Tubes**: Color discharge tubes are devices that emit light when an electric current passes through a gas contained within the tube. The gas ionizes and produces light of a specific color.

2. **Identifying the Gases**: The question provides four options: Neon, Argon, Krypton, and Helium. All these gases are noble gases, which means they are chemically inert and do not react easily with other substances.

3. **Function of the Gas in Discharge Tubes**: The primary role of the gas in a discharge tube is to prevent the filament (often made of tungsten) from burning out. If the tube were filled with air, the oxygen would react with the tungsten filament when heated, leading to its rapid degradation.

4. **Choosing the Right Gas**: Among the noble gases, Argon is the most abundant and cost-effective. It has a low striking voltage and is less reactive, making it an ideal choice for use in color discharge tubes.

5. **Conclusion**: Therefore, the gas that is commonly used in color discharge tubes is Argon.

**Final Answer**: Argon is used in color discharge tubes.

---