On treatment of $100\, mL$ of $0.1\, M$ solution of $CoCl _{3} \cdot 6 H _{2} O$ with excess $AgNO _{3} ; 1.2 \times 10^{22}$ ions are precipitated. The complex is

$\left[ Co \left( H _{2} O \right)_{5} Cl \right] Cl _{2} \cdot H _{2} O$

On treatment of $100\, mL$ of $0.1\, M$ solution of $CoCl _{3} \cdot 6 H _{2} O$ with excess $AgNO _{3} ; 1.2 \times 10^{22}$ ions are precipitated. The complex is}

$\left[ Co \left( H _{2} O \right)_{5} Cl \right] Cl _{2} \cdot H _{2} O$

$\left[ Co \left( H _{2} O \right)_{6}\right] Cl _{3}$

$\left[ Co \left( H _{2} O \right)_{5} Cl \right] Cl _{2} \cdot H _{2} O$

$\left[ Co \left( H _{2} O \right)_{4} Cl _{2}\right] Cl \cdot 2 H _{2} O$

$\left[ Co \left( H _{2} O \right)_{3} Cl _{3}\right] \cdot 3 H _{2} O$

The important postulates as observed by Alfred Werner throughout his experiments are as follows:

The complex/ coordination compounds contain a central metal atom.
The metal atoms in a coordination compound generally show two types of valency: primary valency and secondary valency.
The primary valencies denote the oxidation state. They are ionizable and are satisfied by the negative ions.
Secondary valencies denote the coordination number. They are non-ionizable and are fixed for every metal atom. The secondary valency is generally satisfied by the neutral molecules or negative ions.
The metal atoms should satisfy both primary and secondary valencies.
The secondary valency of the atom basically shows the geometry/ polyhedra of the particular coordination compound.

Though Werner explained some properties of the coordination compound, he failed to explain the colour of the coordinate compound.
He could not explain the magnetic and optical properties of coordination compounds.
He could not answer the question, why does the coordination sphere have a definite geometry.