Answer
$Ag^+$ will pair with $Cl^-$: $AgCl$
$Ba^{2+}$ will pair with $SO_4^{2-}$: $BaSO_4$
$Cu^{2+}$ will pair with $CO_3^{2-}$: $CuCO_3$
$Fe^{3+}$ will pair with $S^{2-}$: $Fe_2S_3$
Work Step by Step
Use the information in table 7.2 (Page 217), to predict the solubility of these compounds:
Rules to remember:
$Cl^-$: Most soluble compounds, except with $Ag^+$, $Pb^{2+}$ and $Hg_2^{2+}$
$SO_4^{2-}$: Most soluble compounds, but the one with $Ba^{2+}$ is an exception.
$CO_3^{2-}$: Most insoluble.
$S^{2-}$: Most insoluble, but the one with $Ba^{2+}$ is an exception.
$Ag^+$:
This cation can form insoluble compounds with : $Cl^-$, $CO_3^{2-}$ and $S^{2-}$.
$Ba^{2+}$:
This cation can form insoluble compounds with: $SO_4^{2-}$ and $CO_3^{2-}$
$Cu^{2+}$:
This cation can form insoluble compounds with: $CO_3^{2-}$ and $S^{2-}$
$Fe^{3+}:$
This cation can form insoluble compounds with: $CO_3^{2-}$ and $S^{2-}$
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So, the $Ag^+$ must pair with $Cl^-$, because it is the only cation that forms a insoluble compound with $Ag^+$: $AgCl$
The $Ba^{2+}$ must pair with $SO_4^{2-}$: $BaSO_4$
The $Fe^{3+}$ and $Cu^{2+}$ can have both $CO_3^{2-}$ or $S^{2-}$; I will choose: $CuCO_3$ and $Fe_2S_3$, but you can switch these ions.
