Consider the following coordination entities: [ Co ( C ₂ O ₄ )₃ ]³⁻ , [ PtCl ₄ ]²⁻ , [ Ni ( CO )₄ ] , [ Fe ( H ₂ O )₆ ]³⁺ , [ Pd ( CN )₄ ]²⁻ , [ Mn ( CN )₆ ]⁴⁻ The number of diamagnetic complexes among the given entities is:

Step-by-step solution

A complex is diamagnetic if it has zero unpaired electrons ( n = 0 ). [ Co ( C ₂ O ₄ )₃ ]³⁻ : Co ³⁺ is 3 d ^6 . Oxalate ( C ₂ O ₄²⁻ ) acts as a strong field ligand with Co ³⁺ . The configuration is t _ 2 g ^6 e _ g ^0 . n = 0 (Diamagnetic). [ PtCl ₄ ]²⁻ : Pt ²⁺ is 5 d ^8 . Metals of the 4 d and 5 d series generally form low-spin square planar complexes with coordination number 4, regardless of ligand strength. n = 0 (Diamagnetic). [ Ni ( CO )₄ ] : Ni is in 0 oxidation state. Its configuration is 3 d ^8 4 s ^2 . In