Which one of the following elements exists as an independent atom in nature under normal conditions?

Options

A. Sodium
B. Iron
C. Helium
D. Oxygen

Answer

To determine which element exists as an independent atom in nature under normal conditions, we need to analyze the options provided based on their electronic configurations and stability.

### Step-by-Step Solution:

1. **Understanding Stability and Bond Formation**:
- Elements tend to form bonds to achieve stability. Stability is often associated with having a complete outer shell of electrons, known as the octet rule. Elements will bond to either gain, lose, or share electrons to attain a noble gas electronic configuration.

2. **Evaluating the Options**:
- **Option 1: Sodium (Na)**:
- Sodium has an electronic configuration of [Ne]3s¹. It has one electron in its outer shell and tends to lose that electron to achieve stability, thus it does not exist independently.
- **Option 2: Iron (Fe)**:
- Iron has an electronic configuration of [Ar]3d⁶ 4s². It can lose electrons to form bonds and does not exist independently in nature.
- **Option 3: Helium (He)**:
- Helium has an electronic configuration of 1s². As a noble gas, it has a complete outer shell and is very stable, allowing it to exist independently as a single atom.
- **Option 4: Oxygen (O)**:
- Oxygen has an electronic configuration of [He]2s² 2p⁴. It needs to gain two electrons to complete its octet, hence it does not exist independently.

3. **Conclusion**:
- Among the given options, **Helium (Option 3)** is the only element that exists as an independent atom under normal conditions due to its complete octet and stability.

### Final Answer:
**Helium (He)** exists as an independent atom in nature under normal conditions.