How many molecules of $EDTA$ (Ethylenediaminetetraacetic acid) are required to form an octahedral complex with a $Ca^{2+}$ ion?

Give the chemical formulas for the following compounds:
$(i)$ Ammonium molybdate
$(ii)$ Ammonium phosphomolybdate
$(iii)$ Ferric thiocyanate ion
$(iv)$ Sodium sulphide

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

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$(IV)$

Which of the following complexes gives only $25\%$ mole of $AgCl$ precipitate when reacted with excess $AgNO_3$?

Provide the classification of ligands.