Which of the following descriptions about `[FeCl_(6)]^(4-)` is correct about the complex ion ?

Options

A. `sp^(3) d` , inner orbital complex , diamagnetic
B. `sp^(3) d^(2)` , outer orbital complex , paramagnetic
C. `d^(2) sp^(3)` , inner orbital complex , paramagnetic
D. `d^(2) sp^(3)` , outer orbital complex , diamagnetic .

Explanation

To determine the correct description of the complex ion \([FeCl_6]^{4-}\), we will follow these steps:

### Step 1: Determine the oxidation state of iron in the complex.
Let the oxidation state of iron be \(x\). Given that chlorine has an oxidation state of \(-1\) and there are 6 chloride ions, the overall charge of the complex is \(-4\).

The equation can be set up as follows:
\[ x + 6(-1) = -4 \]
This simplifies to:
\[ x - 6 = -4 \implies x = +2 \]
Thus, the oxidation state of iron in \([FeCl_6]^{4-}\) is \(+2\).

### Step 2: Write the electronic configuration of iron in the +2 oxidation state.
The atomic number of iron (Fe) is 26. The electronic configuration of neutral iron is:
\[ [Ar] 3d^6 4s^2 \]
When iron loses 2 electrons to become \(Fe^{2+}\), the electrons are removed from the 4s orbital first:
\[ Fe^{2+}: [Ar] 3d^6 \]

### Step 3: Identify the type of hybridization.
Chloride ions (\(Cl^-\)) are weak field ligands, meaning they do not cause pairing of electrons in the d-orbitals. Therefore, the \(3d\) electrons remain unpaired. The hybridization for this complex will involve the \(3d\) orbitals and the \(4s\) and \(4p\) orbitals.

In this case, the hybridization can be described as \(sp^3d^2\) (using two \(d\) orbitals from the \(3d\) level).

### Step 4: Determine the magnetic properties of the complex.
Since there are 6 electrons in the \(3d\) orbitals and they are not paired (due to the weak field nature of the ligands), there will be 4 unpaired electrons.

The presence of unpaired electrons indicates that the complex is paramagnetic.

### Conclusion:
The correct description of the complex ion \([FeCl_6]^{4-}\) is that it is an \(sp^3d^2\) outer orbital complex and is paramagnetic.

### Final Answer:
The correct option is: **SP3-D2 outer orbital complex paramagnetic.**

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