Among the following complexes , which has a magnetic moment of 5.9 BM
`Ni (CO)_(4) [Fe (H_(2)O)_(6)]^(2+),[Co(NH_(3))_(6)]^(3+),[mnBr_(4)]^(2-), [Zn(NH_(3))_(4)]^(2+)`

Options

A. `Ni(CO)_(4)`
B. `[Fe(H_(2) O)_(6)]^(2+)`
C. `[Co(NH_(3))_(6)]^(3+)`
D. `[MnBr_(4)]^(2-)`

Answer

D

Explanation

`Mn^(2+) [Z=25 ]: [Ar] 3d ^(5) : 5 ` unpaired electrons .

`"in" [MnBr_(4)]^(2-)` , five unpaired electrons are present , thus it has magnetic moment of 5.9 BM.