Which of the following statements is not correct?

Options

A. The complexes `[NiCl_(4)]^(2-) and [Ni(CN)_(4)]^(2-)` differ in their magnetic properties
B. The complexes `[Ni(Cl)_(4)]^(2-) and [Ni(CN)_(4)]^(2-)` differ in the state of hybridisation of nickel.
C. The complex `[Ni(Cl)_(4)]^(2-) and [Ni(CN)_(4)]^(2-)` differ in geometry.
D. The complexes `[Ni(Cl)_(4)]^(-2) and [Ni(CN)_(4)]^(2-)` differ in primary valancies of nickel.

Explanation

To determine which statement is not correct regarding the complexes NiCl4^2- and Ni(CN)4^2-, we will analyze each option step by step.

### Step 1: Analyze Option 1
**Statement**: The complexes NiCl4^2- and Ni(CN)4^2- differ in their magnetic properties.

- **Oxidation State**: For both complexes, nickel is in the +2 oxidation state.
- **Ligands**: CN^- is a strong field ligand, while Cl^- is a weak field ligand.
- **Magnetic Properties**:
- Ni(CN)4^2- will have paired electrons (due to strong field ligand), making it diamagnetic.
- NiCl4^2- will have unpaired electrons (due to weak field ligand), making it paramagnetic.

**Conclusion**: This statement is correct.

### Step 2: Analyze Option 2
**Statement**: NiCl4^2- and Ni(CN)4^2- differ in their state of hybridization.

- **Hybridization**:
- Ni(CN)4^2- has DSP2 hybridization (square planar geometry).
- NiCl4^2- has SP3 hybridization (tetrahedral geometry).

**Conclusion**: This statement is correct.

### Step 3: Analyze Option 3
**Statement**: NiCl4^2- and Ni(CN)4^2- differ in geometry.

- **Geometries**:
- Ni(CN)4^2- is square planar.
- NiCl4^2- is tetrahedral.

**Conclusion**: This statement is correct.

### Step 4: Analyze Option 4
**Statement**: NiCl4^2- and Ni(CN)4^2- differ in primary valences of nickel.

- **Primary Valence**: This refers to the oxidation state of the metal.
- **Oxidation State**: In both complexes, nickel has an oxidation state of +2.

**Conclusion**: This statement is incorrect because both complexes have the same primary valence.

### Final Answer
The statement that is not correct is **Option 4**: "These two complexes differ in primary valences of nickel."

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