Which of the following has maximum number of unpaired electron (atomic number of `Fe 26`)

Options

A. Fe
B. Fe (II)
C. Fe (Ill)
D. Fe (IV)

Answer

To determine which of the following has the maximum number of unpaired electrons, we need to analyze the electronic configurations of the given species, particularly focusing on iron (Fe) with an atomic number of 26.

### Step-by-Step Solution:

1. **Identify the Electronic Configuration of Iron (Fe):**
- The atomic number of iron is 26, which means it has 26 electrons.
- The electronic configuration of neutral iron is:
\[ \text{Fe: } [\text{Ar}] 3d^6 4s^2 \]

2. **Determine the Number of Unpaired Electrons in Neutral Iron:**
- In the 3d subshell, we fill the electrons according to Hund's rule, which states that electrons will fill degenerate orbitals singly before pairing up.
- The filling of the 3d subshell for 6 electrons is as follows:
- 1st electron in 3d1
- 2nd electron in 3d2
- 3rd electron in 3d3
- 4th electron in 3d4
- 5th electron in 3d5
- 6th electron pairs with one of the previous electrons.
- Thus, for 3d^6, there are 4 unpaired electrons.

3. **Consider the Fe²⁺ Ion:**
- For Fe²⁺, two electrons are removed from the outermost shell (4s), leading to:
\[ \text{Fe}^{2+}: [\text{Ar}] 3d^6 \]
- The unpaired electrons remain the same as in neutral Fe, which is still 4 unpaired electrons.

4. **Consider the Fe³⁺ Ion:**
- For Fe³⁺, three electrons are removed, resulting in:
\[ \text{Fe}^{3+}: [\text{Ar}] 3d^5 \]
- All five electrons in the 3d subshell are unpaired (1 in each of the five 3d orbitals), giving us 5 unpaired electrons.

5. **Consider the Fe⁴⁺ Ion:**
- For Fe⁴⁺, four electrons are removed, resulting in:
\[ \text{Fe}^{4+}: [\text{Ar}] 3d^4 \]
- In this case, there are 4 unpaired electrons (1 in each of the first four 3d orbitals).

6. **Conclusion:**
- Comparing the number of unpaired electrons:
- Neutral Fe: 4 unpaired electrons
- Fe²⁺: 4 unpaired electrons
- Fe³⁺: 5 unpaired electrons
- Fe⁴⁺: 4 unpaired electrons
- The species with the maximum number of unpaired electrons is **Fe³⁺**, which has **5 unpaired electrons**.

### Final Answer:
The species with the maximum number of unpaired electrons is **Fe³⁺** with **5 unpaired electrons**.

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