Chemistry

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: a. Heated with a few drops of conc.

\text{HNO}_3

b. Treated with excess of

\text{NH}_4\text{Cl}

\text{H}_2\text{S}

gas is passed into solution d. None of these