The number of unpaired electrons presenet in `[NiF_(6)]^(2-)` is ……

Explanation

To determine the number of unpaired electrons in the complex \([NiF_6]^{2-}\), we can follow these steps:

### Step 1: Identify the oxidation state of Nickel
Nickel (Ni) has an atomic number of 28, and its electronic configuration is \( [Ar] 3d^8 4s^2 \). In the complex \([NiF_6]^{2-}\), the overall charge is -2. Since fluorine (F) has a charge of -1 and there are six fluorine ligands, the total negative charge contributed by fluorine is -6. Therefore, the oxidation state of nickel can be calculated as follows:

\[ \text{Oxidation state of Ni} + 6(-1) = -2 \implies \text{Oxidation state of Ni} = +4 \]

### Step 2: Write the electronic configuration of Nickel in the +4 state
When nickel is in the +4 oxidation state, it loses four electrons. The electrons are removed first from the 4s orbital followed by the 3d orbital. Thus, the electronic configuration of nickel in the +4 state is:

\[ 3d^6 4s^0 \]

### Step 3: Determine the geometry and coordination number
The complex \([NiF_6]^{2-}\) has a coordination number of 6, which indicates an octahedral geometry.

### Step 4: Identify the nature of the ligand
Fluorine is a weak field ligand. In general, weak field ligands do not cause significant splitting of the d-orbitals, which would typically lead to unpaired electrons. However, the high oxidation state of nickel will influence the pairing of electrons.

### Step 5: Analyze the crystal field splitting
In an octahedral field, the d-orbitals split into two sets: \(t_{2g}\) (lower energy) and \(e_g\) (higher energy). For nickel in the +4 oxidation state with a \(3d^6\) configuration, the electrons will fill the \(t_{2g}\) orbitals first.

The distribution of the 6 electrons in the d-orbitals will be as follows:
- \(t_{2g}\) orbitals will be fully filled with 6 electrons.
- \(e_g\) orbitals will have 0 electrons.

Thus, the filling will look like this:
- \(t_{2g}^6\)
- \(e_g^0\)

### Step 6: Count the number of unpaired electrons
Since all 6 electrons are paired in the \(t_{2g}\) orbitals and there are no electrons in the \(e_g\) orbitals, we conclude that there are:

\[ \text{Number of unpaired electrons} = 0 \]

### Final Answer
The number of unpaired electrons present in \([NiF_6]^{2-}\) is **0**.

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