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 $H_2S$. The total number of cations precipitated during this reaction is/are :