A complex of a certain metal ion has a magnetic moment of `4.90BM` Another complex of the same metal ion in the same oxidation state has zero magnetic moment The central metal ion could be which of the following (a) `Cr^(3+)` ,(b) `Mn^(3+)` (c ) `Fe^(2+)` (d) `Co^(2+)`
(ii) Refer to the question above if a metal ion has complex ion and with magnetic moments `4.90` and `2.8BM` which one of these is the central metal ion
(a) `Cr^(3+)` (b) `Mn^(3+)` , (c ) `Fe^(2+)` (d) `Co^(2+)` .

Explanation

`mu = 4.90B.M` corresponds to `n =4` which corresponds `d^(6)` configuration In a weak field ligands `d^(6)` configuration will have 4 unpaired electrons In strong field ligands `d^(6)` configuration will have no unpaired electrons with zero magntic moment value `Fe^(2)` have `3d^(6)` configuration In weak field ligands
(b) `mu = 4.9BM` corresponds to `n =4` and for `mu = 2.80BM` corresponds to `n =2`
For `d^(4)` configuration in a weak field ligands it will have 4 unpaired electrons In strong field ligands `d^(4)` configuration will have one paired electrons and two upaireed electrons
Note `d^(1)` to `d^(3)` configuration no pairing will occur whether the ligand field is weak or strong But for d configuration only one pairing will occur in strong field ligands
Therefor `Mn^(3+)` have `3d^(4)` configuration In weak field ligands
.