Write true or false: `[NiCI_(4)]^(2-)` is diamagnetic in nature .

Answer

To determine whether the statement `[NiCl₄]²⁻` is diamagnetic in nature, we need to analyze the oxidation state of nickel, its electronic configuration, and the nature of the ligands involved.

### Step-by-Step Solution:

1. **Determine the Oxidation State of Nickel (Ni)**:
- In the complex `[NiCl₄]²⁻`, let the oxidation state of Ni be \( X \).
- There are 4 chloride ions (Cl⁻), each with a charge of -1. Therefore, the total contribution from the chloride ions is -4.
- The overall charge of the complex is -2.
- The equation can be set up as:
\[ X + 4(-1) = -2 \]
Simplifying this gives:
\[ X - 4 = -2 \implies X = +2 \]
- Thus, the oxidation state of Ni in `[NiCl₄]²⁻` is +2.

2. **Find the Electronic Configuration of Ni²⁺**:
- The atomic number of nickel (Ni) is 28. Its ground state electronic configuration is:
\[ [Ar] 4s^2 3d^8 \]
- When Ni loses 2 electrons to form Ni²⁺, it loses the 4s electrons first:
\[ Ni^{2+}: [Ar] 3d^8 \]

3. **Analyze the Ligands**:
- Chloride ions (Cl⁻) are weak field ligands. They do not cause significant pairing of electrons in the d-orbitals.
- As a result, the 3d electrons will remain unpaired.

4. **Electron Configuration in the Presence of Ligands**:
- In the case of `[NiCl₄]²⁻`, with 4 Cl⁻ ligands, the 3d orbitals will be filled as follows:
- The 3d orbitals will have 8 electrons distributed among them, and due to the weak field nature of Cl⁻, the electrons will occupy the orbitals singly before pairing occurs.
- The 3d configuration will look like this:
- 3d: ↑↓ ↑↓ ↑ ↑ ↑ (2 paired, 6 unpaired)

5. **Count the Number of Unpaired Electrons**:
- In the 3d subshell, there are 2 paired electrons and 6 unpaired electrons.

6. **Determine Magnetic Properties**:
- A complex is **paramagnetic** if it has unpaired electrons and **diamagnetic** if all electrons are paired.
- Since `[NiCl₄]²⁻` has unpaired electrons, it is **paramagnetic**.

### Conclusion:
The statement that `[NiCl₄]²⁻` is diamagnetic is **False**. It is actually paramagnetic due to the presence of unpaired electrons.