Which of the following complexes has magnetic moment of 2.83 Bohr magneton?

Options

A. `[Co(H_2O)_6]Cl_3`
B. `[Ni(H_2O)_6]Cl_2`
C. `[Cu(NH_3)_6]Cl_2`
D. `[Mn(H_2O)_6]Cl_2`

Answer

B

Explanation

2.83 Bohr magneton implies two unpaired electrons according to the expression `sqrt(n(n + 2)mu_B)`. The species Co, Ni, Cu and Mn in the given complexes have `(3d)^6, (3d)^8, (3d)^5` electronic configrations, respectivley. These involve `sp^3d^2, sp^3d^2, sp^3 d^2 and sp^3 d^2`, respectively. Thus, the complex `[Ni(H_2O)_6]^(2+)` has two unpaired electrons.