The colour of $(NH_4)_2SO_4 \cdot Fe_2(SO_4)_3 \cdot 24H_2O$ is

Identify the total number of complexes having bidentate ligands in them from the following list of complexes:
$a$) Tetracyanonickelate$(II)$ ion
$b$) Trioxalatocobaltate$(III)$ ion
$c$) Sodium hexafluoroaluminate$(III)$
$d$) bis(ethylenediamine)dithiocyanatoplatinum$(IV)$

What is the value of the primary valence of $Co$ in $CoCl_{3}$?

The coordination number of cobalt in the complex $[Co(en)_2Br_2]Cl_2$ is

Explain the following term with an example: Hexadentate ligands.

Explain the following term with an example: Hexadentate ligands.