The pair in which both species have same magnetic moment (spin only value) is .

Options

A. `[Cr(H_(2)O)_6]^(2+)` , `[CoCl_4]^(2-)`
B. `[Cr(H_(2)O)_6]^(2+)` , `[Fe(H_(2)O)_6]^(2+)`
C. `[Mn(H_(2)O)_6]^(2+)` . `[Cr(H_(2)O)_6]^(2+)`
D. `[CoCl_4]^(2-)`, `[Fe(H_(2)O)_6]^(2+)`

Answer

B

Explanation

Species having same magnetic moment must also have same number of unpaired electrons
`Co^(2+)(3d^(7))` = 3 unpaired electrons
`Cr^(2+)(3d^(5))` = 4 unpaired electrons
`Mn^(2+)(3d^(5))` = 5 unpaired electrons
`Fe^(2+)(3d^(6))` = 4 unpaired electrons.
Therefore (b) is the correct option.