Crystal field theory provides correct electronic distribution of central metal under surrounding ligannd field, hence it clearly explains magnetic moment, colour of a complex.
Q. Which of the following complex is high spin?

Options

A. `K_(4)[Fe(CN)_(6)]^(-)`
B. `[PtCl_(4)]^(2-)`
C. `[CoF_(6)]^(3-)`
D. `[Ni(NH_(3))_(6)]^(2+)`

Answer

C

Explanation

`K_(4)[Fe(CN)_(6)]`: Low spin complex: `P lt Delta_(0)`
`[PtCl_4]^(2-)`:Los spin complex: `P lt Delta_(0)`
`[CoF_(6)]^(3-)`: High spin complex: `P gt Delta_(0)`
`[Ni(NH_(3))_(6)]^(2+)`: High spin or low spini not defined.