Answer
$\begin{array}
{|c|cc|}
\hline
&NH_4^+&Ni^{2+} \\
\hline
CO_3^{2-} &(NH_4)_2CO_3& NiCO_3 \\
SO_4^{2-} &(NH_4)_2SO_4&NiSO_4 \\
\hline
\end{array}$
Work Step by Step
$\begin{array}
{|c|cc|}
\hline
&NH_4^+&Ni^{2+} \\
\hline
CO_3^{2-} &(NH_4)_2CO_3& NiCO_3 \\
SO_4^{2-} &(NH_4)_2SO_4&NiSO_4 \\
\hline
\end{array}$
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.
