Answer:
An atom's coordination number in a molecule refers to the number of atoms attached with the central atom. The coordination number in chemistry illustrates the number of neighbor atoms in regard to a central atom. The coordination number can differ from as low as two to as high as sixteen. The value of the coordination number relies upon the comparative sizes of the central atoms and the ligands and by the charge from the ion's electronic configuration.
The NH₃ is a neutral ligand. Thus, the formula for a complex produced in between Ni²⁺ and NH₃ with a coordination number 5 will be [Ni(NH₃)₅]²⁺.