Which of the following is not a noble gas?

Options

A. helium
B. neon
C. argon
D. hydrogen

Explanation

To determine which of the following is not a noble gas, we need to understand what noble gases are and their characteristics.

### Step-by-Step Solution:

1. **Identify Noble Gases**: Noble gases are a group of elements found in Group 18 of the periodic table. They are known for having a complete outer shell of electrons, which makes them very stable and unreactive.

2. **List Common Noble Gases**: The common noble gases include:
- Helium (He) - Atomic number 2
- Neon (Ne) - Atomic number 10
- Argon (Ar) - Atomic number 18
- Krypton (Kr) - Atomic number 36
- Xenon (Xe) - Atomic number 54
- Radon (Rn) - Atomic number 86

3. **Check the Options**: Now, we need to check the options provided in the question to see which one does not belong to the noble gas category.

4. **Analyze Each Option**:
- **Option 1**: Helium (He) - This is a noble gas.
- **Option 2**: Neon (Ne) - This is a noble gas.
- **Option 3**: Argon (Ar) - This is a noble gas.
- **Option 4**: Hydrogen (H) - This is not a noble gas. Hydrogen has only one electron and does not have a complete outer shell.

5. **Conclusion**: Since hydrogen does not have a complete outer shell of electrons and is not part of the noble gases, the answer to the question "Which of the following is not a noble gas?" is **Hydrogen**.

### Final Answer:
**Hydrogen is not a noble gas.**