Among the following hexaaqua complexes, the number of complexes having a spin-only magnetic moment of approximately 4.90 BM is [ V ( H ₂ O )₆]²⁺ , [ Cr ( H ₂ O )₆]²⁺ , [ Mn ( H ₂ O )₆]²⁺ , [ Fe ( H ₂ O )₆]²⁺ , [ Co ( H ₂ O )₆]²⁺ , [ Ni ( H ₂ O )₆]²⁺

Step-by-step solution

The spin-only magnetic moment is given by = n(n+2) BM , where n is the number of unpaired electrons. For 4.90 BM , n(n+2) = 4.90 n(n+2) 24 , which gives n = 4 . In all the given complexes, the ligand H ₂ O acts as a weak field ligand, leading to high-spin configurations for the central metal ions. 1. [ V ( H ₂ O )₆]²⁺ : V ²⁺ is 3d^3 ( t_ 2g ^3 e_g^0 ) n = 3 2. [ Cr ( H ₂ O )₆]²⁺ : Cr ²⁺ is 3d^4 ( t_ 2g ^3 e_g^1 ) n = 4 3. [ Mn ( H ₂ O )₆]²⁺ : Mn ²⁺ is 3d^5 ( t_ 2g ^3 e_g^2 ) n = 5 4. [ Fe ( H ₂ O )₆]²⁺ : Fe ²⁺ is 3