To avoid the precipitation of hydroxides of  ${\mathrm{Ni}}^{2+},{\mathrm{Co}}^{2+},{\mathrm{Mn}}^{2+}$ along with those of the third group cations, then solutions should be
 

Function of strong electrolyte NH₄Cl is to suppress the ionisation of NH₄OH so that the concentration of OH- ions in the solution is decreased but it is sufficient to precipitate the third group basic radicals because the solubility product of group III hydroxides is lower than IV, V and VI group hydroxides.