To avoid the precipitation of hydroxides of `Ni^(2+),Co^(2+),Zn^(2+) and Mn^(2+)` along with those of `Fe^(3+),Al^(3+) and Cr^(3+)` the third group cations, solution should be:

Options

A. Heated with a few drops of conc. `HNO_(3)`
B. Treated with excess of `NH_(4)Cl`
C. `H_(2)S` gas is passed into solution
D. None of these

Answer

B

Explanation

The value of `K_(sp)` of hydroxides of `Fe^(3+),Cr^(3+),Al^(3+)` are lower than that of `Co^(2+),Ni^(2+),Mn^(2+) and Zn^(2+)` Therefore, in the presence of `NH_(4)Cl`, dissociation of `NH_(4)OH` suppressed and conc. Of `OH^(-)`, furnished from `NH_(4)OH`, is such that only third roup basic radicals are precipitate.