We may assume that Ni2+ is associated with an anion such as NO3- or Cl-. Nickel nitrate and nickel chloride are soluble compounds in water.
When concentrated ammonia solution is added to the aqueous green colour Ni2+ solution ( Ni(NO3)2 or NiCl2 ), blue colour hexaamminenickel(ii) ion ( [Ni(NH3)6]2+ ) is given.
If dilute ammonia solution is added instead of concentrated ammonia solution, first a green colour precipitate is given. When ammonia solution is added more, you can see that green colour precipitate dissolve and give blue colour solution.
This is a testing experiment of Ni2+ ion.
Then saturated NaBr colourless solution is added to the [Ni(NH3)6]2+ solution. Now aqueous solution includes following cations, anions and molecules.
If Ni2+ and Br- concentrations are high, NiBr2 can be precipitated and it is a yellowish-green odorless solid.
If aqueous dilute ammonia solution is added to the Ni2+ ion, a green precipitate, nickel hydroxide ( Ni(OH)2) is given.
We can see nothing as colour change, dissolving, gas releasing etc. Green precipitate exists without change. So there is no effect (reaction) with NaOH or ecxess NaOH.
To form the coordination complex, there should be excess NH3 molecules. Therefore, concentrated ammonia solution is required to provide excess NH3.
Yes. It is possible.