For the purpose of systematic qualitative analysis, cations are classified into various groups on the basisof their behaviour against some reagents. The group reagents used for the classification of most common cations are hydrochloric acid, hydrogen sulphide, ammonium hydroxide, and ammonium carbonate. Classification id based on wheather a certain reacts with these reagents by the formation of precipitates or not.
To avoid the precipitation of hydroxides of `Ni^(2+),Co^(2+),Mn^(2+)` along with those of the third group cations, the solutions should be :

Options

A. Heated with few drops of concentrated `HNO_3`
B. Boiled with excess of ammonium chloride
C. Concentrated to small volume
D. None of these

Answer

B

Explanation

Function of strong electrolyte `NH_4Cl` is to suppress 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 prouduct of group III hydrooxides is lower than IV, V and VI group hydroxides. The `Cr(OH)_3darr` is slightly soluble in excess of precipitant , upon boiling the solution, `Cr(OH)_3` is precipitated.