NiCl2.6H2O on reacting with excess AgNO3, it gives 2 moles of AgCl. This indicates that the 2Cl− ions in the complex is not bounded by the coordination sphere and hence are present as counter ions of the complex.
Thus, the coordination complex is [Ni(H2O)6]2+ 2Cl−.
Thus, 6 water molecules are bounded to the Ni and hence, the coordination number is 6.