The magnetic moment of [CoCl₄]2− is approximately: (Co atomic number = 27)
Co₂+ (d7) in [CoCl₄]2− (tetrahedral) with weak field Cl− is high spin (3 unpaired). μ ≈ 3.87 BM.
Ref: NCERT Class 12 Chemistry > Chapter 5: Coordination Compounds > Topic: Colour and Magnetic Properties and Stability and Importance