On the basic of `CET` explaine the following complex of `Co^(3+)` like `[Co(NH_(3))_(6)]^(3+),[Co(en)_(3)]^(3+)` and `[Co(NO_(2))_(6)]^(3-)`
are diamagntic while `[CoF_(6)]^(3-)` and `[Co(H_(2)O)_(6)]^(3+)` are paramagnetic .

Explanation

The complex ions viz `[Co(NH_(3))_(6)]^(3+),[Co(en)_(3)]^(3+)`
and `[Co(NO_(2))_(6)]^(3-)` have `Co^(3+0` ion `(3d^(6) "ins")` as their central metal atom ion and have `NH_(3)` en and `NO_(2)^(Θ)` as ligands Since these ligands are strong field ligands, the distribution of `3d^(6)` electrons of `Co^(3+)` ion in `t_(2g)` and `e_(g)` orbitals take place in such a way that all `3d^(6)` electrons become paired in `t_(2g)` orbitals and `e_(g)` orbitals remain vacant as shown

Therefore all are diamagnetic with `n=0`
`[CoF_(6)]^(3-)` and `[Co(H_(2)O)_(6)]^(3+)` also have `Co^(3+)` ion `(3d^(6)"ion")`
and `F^(Θ)` and `H_(2)O` as weak field ligands The distribution of electrons in `t_(2g)` and `e_(g)` are as shown:

Therefore these two complexes are paramagnetic with `n=4`
`mu_("spin") =sqrt(24) BM` .