Source of most of the noble gases is ____________.

Explanation

**Step-by-Step Solution:**

1. **Identify the Group of Elements**: The noble gases belong to Group 18 of the periodic table, which includes Helium, Neon, Argon, Krypton, Xenon, and Radon.

2. **Sources of Noble Gases**: Most noble gases are found in the atmosphere. They are present in trace amounts, with Argon being the most abundant among them.

3. **Occurrence of Noble Gases**:
- Helium and Neon can be found in certain minerals.
- Radon is a radioactive element and is the rarest of the noble gases.

4. **Extraction Method**: The noble gases, except for Radon, can be extracted from the air. This is done through a process of liquefaction followed by fractional distillation.

5. **Conclusion**: Therefore, the source of most of the noble gases is the atmosphere.

**Final Answer**: Source of most of the noble gases is **the atmosphere**.

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