Which of the following is the correct electronic configuration of `Fe^(3+)` ion ? (Z for Fe = 26)

Options

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

Answer

To determine the correct electronic configuration of the `Fe^(3+)` ion, we will follow these steps:

### Step 1: Identify the Atomic Number of Iron
The atomic number (Z) of iron (Fe) is 26. This means that a neutral iron atom has 26 electrons.

### Step 2: Write the Electronic Configuration of Neutral Iron
The electronic configuration of neutral iron (Fe) can be written as follows:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²

### Step 3: Determine the Charge of the Ion
The `Fe^(3+)` ion indicates that iron has lost 3 electrons.

### Step 4: Remove Electrons to Form the Ion
When forming the `Fe^(3+)` ion, we remove electrons starting from the outermost shell. The order of removal is:
1. Remove 2 electrons from the 4s orbital.
2. Remove 1 electron from the 3d orbital.

After removing these electrons, the configuration changes as follows:
- From 4s², we remove 2 electrons → 0 electrons left in 4s.
- From 3d⁶, we remove 1 electron → 3d⁵ remains.

### Step 5: Write the Electronic Configuration of `Fe^(3+)`
After removing the electrons, the electronic configuration of `Fe^(3+)` becomes:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵

### Step 6: Compare with Given Options
Now, we compare this configuration with the provided options to find the correct one:
1. 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴ 4s¹ (Incorrect)
2. 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s² (Incorrect)
3. 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ (Correct)
4. 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s² 4p³ (Incorrect)

### Final Answer
The correct electronic configuration of the `Fe^(3+)` ion is:
**1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵**

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