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