Explain with two examples the following
Central atom or ion.

Explanation

Central `"atom"//"ion"` : In a coordination entity the `"atom"//"ion"` to which a fixed number of `"ions"//"groups"` are bound in a definite geometrical arrangement around it, is called the central atom or ion.
For example, the central `"atom"//"ion"` in the coordination entities : `[NiCl_2 (H_2O)_4]`. `[COCl(NH_3)_5]^(2+)` and `[Fe(CN)_6]^(3+)` are `Ni^(2+), Co^(3+)` and `Fe^(3+)` respectively. These central `"atoms"//"ions"` are also referred to as Lewis acids.