Sources of inert gases are 

Options

A. Air
B. Natural gas
C. Minerals
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding Inert Gases**: Inert gases, also known as noble gases, include helium, neon, argon, krypton, xenon, and radon. These gases are characterized by their lack of reactivity due to having a complete valence shell of electrons.

2. **Identifying Sources**: To determine the sources of inert gases, we can explore various natural and artificial sources.

3. **Air as a Source**:
- Air is a mixture of gases, and it contains approximately 0.93% argon, which is an inert gas. Therefore, air is a significant source of inert gases.

4. **Natural Gas as a Source**:
- Natural gas primarily consists of methane, but it can also contain small amounts of inert gases such as helium and nitrogen. The concentration of these gases is typically less than 1%.

5. **Minerals as a Source**:
- Certain minerals, such as pitch blend and monazite, can contain traces of noble gases. These gases are often trapped within the mineral structure and can be extracted.

6. **Conclusion**: Based on the above points, we can conclude that the sources of inert gases include air, natural gas, and certain minerals. Therefore, the correct answer is "all of the above."

---