Select the correct statements among the following.

Options

A. Co (III) is stabilised in presence of weak field ligands, while Co (II) is stabilised in presence of strong field ligabd,
B. Four coordinated complexes of Pd(II) and Pt(II) are paramagnetic and square planar.
C. `[Ni(CN)_(4)]^(4-)` ion and `[Ci(CO)_(4)]` are tetrahedral and square planar respectively.
D. `Ni^(2+)` ion does not form inner orbital octahedral complexes in presence of weak ligand fields.

Answer

To solve the question of selecting the correct statements, we will analyze each option provided in the question step by step.

### Step 1: Analyze Option 1
**Statement:** Cobalt III is stabilized in presence of a weak field ligand, while Cobalt II is stabilized in presence of a strong field ligand.

**Analysis:**
- Cobalt(III) (Co³⁺) has a configuration of 3d⁶. In the presence of a weak field ligand, the electrons will occupy higher energy orbitals, leading to less stabilization.
- Cobalt(II) (Co²⁺) has a configuration of 3d⁷. It is generally stabilized by strong field ligands which cause pairing of electrons in the lower energy orbitals.
- Therefore, this statement is **incorrect**.

### Step 2: Analyze Option 2
**Statement:** Four coordinated complexes of palladium(II) and platinum(II) are paramagnetic and square planar.

**Analysis:**
- Palladium(II) (Pd²⁺) and platinum(II) (Pt²⁺) both have a d⁸ configuration. They typically form square planar complexes due to their higher effective nuclear charge (Z effective).
- However, these complexes are **not paramagnetic**; they are actually diamagnetic because all electrons are paired in the square planar geometry.
- Thus, this statement is **incorrect**.

### Step 3: Analyze Option 3
**Statement:** Ni(CN)₄²⁻ is a square planar complex and Ni(CO)₄ is tetrahedral.

**Analysis:**
- In Ni(CN)₄²⁻, nickel is in the +2 oxidation state (3d⁸). CN⁻ is a strong field ligand, which leads to pairing of electrons and the formation of a square planar complex (DSP² hybridization).
- In Ni(CO)₄, nickel is in the zero oxidation state (3d⁸ 4s²). CO is also a strong field ligand, but it leads to the formation of a tetrahedral complex (sp³ hybridization).
- Therefore, this statement is **incorrect** as the configurations are reversed.

### Step 4: Analyze Option 4
**Statement:** Ni²⁺ ions do not form inner orbital complexes; they form outer orbital complexes in the presence of weak field ligands.

**Analysis:**
- Ni²⁺ has a 3d⁸ configuration. In the presence of weak field ligands, the electrons do not pair up and occupy the higher energy orbitals (outer orbitals).
- Thus, Ni²⁺ indeed does not form inner orbital complexes but rather outer orbital complexes in the presence of weak field ligands.
- Therefore, this statement is **correct**.

### Conclusion
The only correct statement among the options provided is **Option 4**.

---