Which of the following electron configurations is correct for iron,(atomic number26)?

Options

A. `1s^(2), 2s^(2)2p^(6), 3s^(2)3p^(6) 3d^(5)`
B. `1s^(2), 2s^(2)2p^(6), 3s^(2)3p^(6), 4s^(2), 3d^(5)`
C. `1s^(2), 2s^(2)2p^(6), 3s^(2)3p^(6), 4s^(2), 3d^(7)`
D. `1s^(2), 2s^(2) 2p^(6), 3s^(2)3p^(6)3d^(6), 4s^(2)`

Explanation

To determine the correct electron configuration for iron (atomic number 26), we can follow these steps:

### Step 1: Understand the Atomic Number
Iron has an atomic number of 26, which means it has 26 electrons.

### Step 2: Fill the Electron Shells
We will fill the electron shells according to the Aufbau principle, which states that electrons fill orbitals starting from the lowest energy level to the highest.

1. **1s Orbital:** Can hold 2 electrons.
- Configuration: 1s²
2. **2s Orbital:** Can hold 2 electrons.
- Configuration: 1s² 2s²
3. **2p Orbital:** Can hold 6 electrons.
- Configuration: 1s² 2s² 2p⁶
4. **3s Orbital:** Can hold 2 electrons.
- Configuration: 1s² 2s² 2p⁶ 3s²
5. **3p Orbital:** Can hold 6 electrons.
- Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶
6. **4s Orbital:** Can hold 2 electrons and is filled before the 3d orbital because it has a lower energy level.
- Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
7. **3d Orbital:** After filling the 4s orbital, we fill the 3d orbital with the remaining electrons. Iron has 26 electrons, and we have already used 24 electrons in the previous orbitals, leaving us with 2 electrons to place in the 3d orbital.
- Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

### Final Electron Configuration
Thus, the complete electron configuration for iron (atomic number 26) is:
**1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶**

### Conclusion
The correct electron configuration for iron is **1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶**.

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