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 the conditions under which a ligand is classified as a weak field ligand based on the crystal field stabilization energy (Δ₀) and the pairing energy (P), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Crystal Field Stabilization Energy (Δ₀)**: This is the energy difference between the lower energy (t₂g) and higher energy (eₕ) orbitals in an octahedral field.
- **Pairing Energy (P)**: This is the energy required to pair two electrons in the same orbital.

2. **Identify the Electron Configuration**:
- In an octahedral complex, the d-orbitals split into two sets: t₂g (lower energy) and eₕ (higher energy).
- When filling these orbitals, electrons will first occupy the lower energy t₂g orbitals before pairing occurs.

3. **Determine the Condition for Weak Field Ligands**:
- A ligand is classified as a weak field ligand if the energy required to pair electrons (P) is greater than the crystal field splitting energy (Δ₀).
- This means that when the fourth electron is added, it is energetically more favorable for it to occupy the higher energy eₕ orbital rather than pairing with an electron in the t₂g orbital.

4. **Conclusion**:
- Therefore, the condition for a ligand to be classified as a weak field ligand is:
\[ P > Δ₀ \]
- This indicates that the energy cost of pairing is higher than the energy gained from the splitting, leading to the preference for occupying the higher energy orbitals.

### Final Answer:
A ligand is called a weak field ligand if the pairing energy (P) is greater than the crystal field stabilization energy (Δ₀).