A: The degeneracy of d-orbitals is lost under strong field ligand
R: The degeneracy of d-orbitals does not get lost under weak field ligand

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. ) If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To analyze the given assertion and reason regarding the degeneracy of d-orbitals in the presence of strong and weak field ligands, we can break down the explanation into a step-by-step solution.

### Step-by-Step Solution:

**Step 1: Understanding Degeneracy of d-Orbitals**
- **Definition**: 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 degenerate when isolated, meaning they all have the same energy.

**Step 2: Effect of Ligands on d-Orbitals**
- **Ligand Interaction**: When ligands approach a metal ion, they interact with the d-orbitals. The nature of this interaction depends on whether the ligands are strong field or weak field ligands.
- **Strong Field Ligands**: Strong field ligands cause a significant splitting of the d-orbitals due to stronger interactions, leading to a loss of degeneracy. This means that the energy levels of the d-orbitals become unequal.
- **Weak Field Ligands**: Weak field ligands cause a smaller degree of splitting, but they also result in a loss of degeneracy, albeit to a lesser extent than strong field ligands.

**Step 3: Conclusion on Assertion and Reason**
- **Assertion (A)**: "The degeneracy of d-orbitals is lost under strong field ligand." - This statement is **True** because strong field ligands cause significant splitting of the d-orbitals.
- **Reason (R)**: "The degeneracy of d-orbitals does not get lost under weak field ligand." - This statement is **False** because weak field ligands also cause a loss of degeneracy, just to a lesser extent than strong field ligands.

**Final Conclusion**: The assertion is true, but the reason is false. Therefore, the correct answer is that the assertion is true, but the reason provided is not correct.