## Chemistry and Chemical Reactivity (9th Edition)

$\begin{array} {|c|cc|} \hline &NH_4^+&Ni^{2+} \\ \hline CO_3^{2-} &(NH_4)_2CO_3& NiCO_3 \\ SO_4^{2-} &(NH_4)_2SO_4&NiSO_4 \\ \hline \end{array}$
$\begin{array} {|c|cc|} \hline &NH_4^+&Ni^{2+} \\ \hline CO_3^{2-} &(NH_4)_2CO_3& NiCO_3 \\ SO_4^{2-} &(NH_4)_2SO_4&NiSO_4 \\ \hline \end{array}$ With ammonium, since its charge is +1, 2 cations are required to balance the -2 charges of the anions. The other combinations have a +2 cation and a -2 anion, so their proportion must be 1:1.