If`Delta_(0)` is the crystal field stabilisation energy of a ligand and P is the energy required for electron pairing in an orbital, then ligand is called weak ligand if

Options

A. `Delta_(0)gtP`
B. `Delta_(0)ltP`
C. `Delta_(0)=P`
D. Unpredictable

Answer

To determine when a ligand is classified as a weak ligand based on the crystal field stabilization energy (Δ0) and the energy required for electron pairing (P), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Δ0 (Crystal Field Stabilization Energy)**: This is the energy difference between the split d-orbitals in a complex due to the presence of ligands.
- **P (Pairing Energy)**: This is the energy required to pair two electrons in the same orbital.

2. **Consider Electron Configuration**:
- When d-orbitals are split in the presence of ligands, electrons can either occupy the lower energy orbitals (t2g) or the higher energy orbitals (eg).
- For example, in a d4 configuration, the fourth electron can either pair with an existing electron in the lower energy orbital or occupy a higher energy orbital.

3. **Analyze the Conditions for Pairing**:
- If the energy required for pairing (P) is less than the energy gap (Δ0), then it is energetically favorable for the electrons to pair up in the lower energy orbitals. This situation corresponds to a **strong field ligand**.
- Conversely, if the energy required for pairing (P) is greater than the energy gap (Δ0), then it is more favorable for the electrons to occupy the higher energy orbitals rather than pair up. This situation corresponds to a **weak field ligand**.

4. **Formulate the Condition**:
- A ligand is classified as a weak ligand if:
\[ P > Δ0 \]
- This means that the energy required to pair electrons is greater than the energy gained from the crystal field stabilization.

5. **Conclusion**:
- Therefore, if the pairing energy (P) is greater than the crystal field stabilization energy (Δ0), the ligand is termed a weak ligand.

### Final Answer:
A ligand is called a weak ligand if \( P > Δ0 \).