Answer
$Ni(NO_3)_2+Na_2CO_3\rightarrow NiCO_3+2\ NaNO_3$
$Ni^{2+}(aq)+CO_3^{2+}(aq)\rightarrow NiCO_3(s)$
Work Step by Step
Balancing the sodiums:
$Ni(NO_3)_2+Na_2CO_3\rightarrow NiCO_3+2\ NaNO_3$
Which is the fully balanced equation.
Since nickel (||) carbonate is the only insoluble compound, the net ionic equation is:
$Ni^{2+}(aq)+CO_3^{2+}(aq)\rightarrow NiCO_3(s)$
