The coordination number of $Cu$ in $[Cu(H_2O)_4]^{2+}$ is ...... .

Coordination number of $Fe$ in the complexes $[Fe(CN)_6]^{4-}$,$[Fe(CN)_6]^{3-}$ and $[FeCl_4]^{-}$ would be respectively

The coordination number of a central metal atom in a complex can be determined by $......$.

The name of the ring structure complex compound formed between a metal ion and a polydentate ligand is . . . . . . .

The secondary valences (coordination numbers) of the following complexes based on their reactions with excess $AgNO_3$ are:

Formula of the complexes	Moles of $AgCl$ precipitated per mole of complex
$(I) \ CoCl_3 \cdot 6 H_2O$	$3$
$(II) \ NiCl_3 \cdot 6 H_2O$	$2$
$(III) \ Co(SO_4)Br \cdot 5 NH_3$	$1$

Find the secondary valences for $(I), (II),$ and $(III)$ respectively.

In the complex ion $[Co(NH_3)_6]^{3+}$,the $NH_3$ molecules are linked to the metal atom by .......