Explain the terms: Coordination Number,Coordination Sphere,and Coordination Polyhedron.

(N/A) Coordination Number: The number of ligand donor atoms to which the metal is directly bonded is called the coordination number. For example,in the complex ions $[PtCl_6]^{2-}$ and $[Ni(NH_3)_4]^{2+}$,the coordination numbers of $Pt$ and $Ni$ are $6$ and $4$ respectively. In $[Fe(C_2O_4)_3]^{3-}$ and $[Co(en)_3]^{3+}$,the coordination number of $Fe$ and $Co$ is $6$.
Coordination Sphere: The central atom/ion and the ligands attached to it are enclosed in a square bracket and are collectively termed as the coordination sphere.
The groups that ionize are written outside the bracket and are called counter ions. For example,in the complex $K_4[Fe(CN)_6]$,$[Fe(CN)_6]^{4-}$ is the coordination sphere and $K^+$ is the counter ion.
Coordination Polyhedron: The spatial arrangement of the ligand atoms which are directly attached to the central atom/ion defines the geometry of the coordination polyhedron.