To an aqueous solution containing ions such as Al^3+, Zn^2+, Ca^2+, Fe^3+, Ni^2+, Ba^2+ and Cu^2+ was added conc. HCl, followed by H_2 S. The total…

To an aqueous solution containing ions such as $\displaystyle \mathrm{Al}^{3+}, \mathrm{Zn}^{2+}, \mathrm{Ca}^{2+}, \mathrm{Fe}^{3+}, \mathrm{Ni}^{2+}, \mathrm{Ba}^{2+}$ and $\displaystyle \mathrm{Cu}^{2+}$ was added conc. HCl , followed by $\displaystyle \mathrm{H}_2 \mathrm{~S}$.The total number of cations precipitated during this reaction is/are :