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. \( \mathrm{HCl} \), following by \( \mathrm{H_2S} \).
The Total number of cations precipitated during this reaction is/are:
