Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The complex ion [Co(C₂O₄)₃]³⁻ is diamagnetic in nature. Reason (R): Oxalate ion ( C₂O₄²⁻ ) is a weak field ligand and forms a high-spin complex with Co³⁺ . In the light of the above statements, choose the most appropriate answer from the options given below.

Step-by-step solution

The oxidation state of cobalt in [Co(C₂O₄)₃]³⁻ is +3 . The electronic configuration of Co³⁺ is 3d^6 . Generally, oxalate ( C₂O₄²⁻ ) is a weak field ligand as it is an oxygen donor. However, with Co³⁺ , it acts as a strong field ligand. This is an important exception in the spectrochemical series. Due to the strong field nature of oxalate with Co³⁺ , the pairing energy is less than the crystal field splitting energy ( _o > P ). The 3d^6 electrons pair up completely in the t_ 2g orbitals, giving the configuration t_