To avoid the precipitation of hydroxides of ,

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Problem

To avoid the precipitation of hydroxides of

\text{Ni}^{2+}

\text{Co}^{2+}

\text{Zn}^{2+}

and

\text{Mn}^{2+}

along with those of

\text{Fe}^{3+}

\text{Al}^{3+}

and

\text{Cr}^{3+}

the third group solution should be: (1) Heated with a few drops of conc.

\text{HNO}_3

(2) Treated with excess of

\text{NH}_4\text{Cl}

(3)

\text{H}_2\text{S}

gas is passed into solution (4) None of these