Assertion: Transition metal ion forming octahedral complexes undergo `sp^(3)d^(2) or d^(2) sp^(3)` hybridisation.
Reason: Strong field ligands force the unpaired electrons of central metal ion to pair up causingg `d^(2)sp^(3)` hybridisation whereas weak field ligands do not affect electronic configuration of the metal ion undergoes in `sp^(3)d^(2)` hybridisation.

Options

A. If assertion is true but the reason is false
B. If assertion is false but reason is true
C. If both assertion and reason are true and the reason is the correct explanation of assertion
D. If both assertion and reason are true but reason is not the correct explanation of assertion

Answer

To solve the question regarding the assertion and reason related to transition metal ions forming octahedral complexes, we can break it down into a step-by-step analysis.

### Step 1: Understanding the Assertion
The assertion states that transition metal ions forming octahedral complexes undergo \( sp^3d^2 \) or \( d^2sp^3 \) hybridization.

**Explanation**:
- In an octahedral complex, the central metal ion is surrounded by six ligands.
- The hybridization that occurs is a combination of one s orbital, three p orbitals, and two d orbitals, resulting in either \( sp^3d^2 \) or \( d^2sp^3 \) hybridization depending on the nature of the ligands.

### Step 2: Analyzing the Reason
The reason states that strong field ligands force the unpaired electrons of the central metal ion to pair up, resulting in \( d^2sp^3 \) hybridization, while weak field ligands do not affect the electronic configuration, leading to \( sp^3d^2 \) hybridization.

**Explanation**:
- Strong field ligands (like CN⁻, CO) cause pairing of electrons in the d orbitals. This means that some of the unpaired electrons will pair up, allowing for \( d^2sp^3 \) hybridization.
- Weak field ligands (like H₂O, Cl⁻) do not cause such pairing, and thus the electrons remain unpaired, leading to \( sp^3d^2 \) hybridization.

### Step 3: Conclusion
Both the assertion and reason are correct. The reason provided accurately explains the assertion regarding the hybridization of transition metal ions in octahedral complexes.

### Final Answer
- **Assertion**: Correct
- **Reason**: Correct
- **Explanation**: The reason is the correct explanation of the assertion.