The degeneracy of d-orbitals is lost under:
(I) Strong field ligand
(II) Weak field ligand
(III) Mixed field lagand
(IV) Chelated Ligand field
Choose the correct code:

Options

A. I, II and IV
B. I and II
C. I, II, III and IV
D. I, II and III

Explanation

To solve the question regarding the loss of degeneracy of d-orbitals under different ligand fields, we will analyze each option step by step.

### Step 1: Understand Degeneracy of d-Orbitals
Degeneracy refers to the condition where multiple orbitals have the same energy level. In the case of d-orbitals, there are five orbitals (dxy, dyz, dxz, dx²-y², dz²) that are normally degenerate (equal in energy) in a free metal ion.

**Hint:** Remember that degeneracy is a characteristic of energy levels in quantum mechanics.

### Step 2: Analyze the Effect of Ligands
When ligands approach a central metal ion, they create an electric field that affects the energy levels of the d-orbitals. Depending on the nature of the ligands (strong field or weak field), the d-orbitals can split into different energy levels.

**Hint:** Consider how the strength of the ligand influences the splitting of d-orbitals.

### Step 3: Strong Field Ligands
Strong field ligands cause a significant splitting of the d-orbitals, leading to a loss of degeneracy. This means that the energy levels of the d-orbitals become unequal.

**Hint:** Strong field ligands lead to large splitting, thus affecting degeneracy.

### Step 4: Weak Field Ligands
Weak field ligands cause less splitting of the d-orbitals compared to strong field ligands. However, they still induce some degree of splitting, which means that degeneracy is also lost, but to a lesser extent.

**Hint:** Weak field ligands also affect degeneracy, but the effect is smaller.

### Step 5: Mixed Field Ligands
Mixed field ligands can exhibit characteristics of both strong and weak field ligands. Depending on the specific ligands involved, they can lead to varying degrees of splitting and loss of degeneracy.

**Hint:** Mixed field ligands can have complex effects on degeneracy.

### Step 6: Chelated Ligands
Chelated ligands, which form multiple bonds with the metal ion, can also lead to significant splitting of the d-orbitals, resulting in a loss of degeneracy.

**Hint:** Chelated ligands often create strong interactions, which can affect degeneracy.

### Conclusion
From the analysis, we can conclude that the degeneracy of d-orbitals is lost under all the conditions mentioned: strong field ligands, weak field ligands, mixed field ligands, and chelated ligands. Therefore, the correct answer is **(I), (II), (III), and (IV)**.

### Final Answer
The correct code is **(I), (II), (III), (IV)**.