# To aviod the precipitation of hydroxide of $Ni^{2+}, Co^{2+}, Mn^{2+}$ along with those of the third group cations, the solutions should be

(a) Heated with few drops of conc. $HNO_3$
(b) Heated with excess of ammonium chloride
(c) Concentrated to small volume
(d) None of these

Answer: Heated with excess of ammonium chloride

Function of strong electrolyte $NH_4Cl$ is to supress the ionisation of $NH_4OH$ 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.