Equation for salt formation for ammonium oxalate?
Where am I wrong? First of all, note that the ammonia is dissolved in water. So there is an ion that's involved in the reaction, not the ammonia itself. And second, the charge of the ion involved requires a different coefficient for ammonia. Notice that the $\ce{H+}$ cations in Hydrogen oxalate are spectator ions.

The formation of Ammonium Oxalate will be a precipitation reaction. (Or some may put it an acid-base one) Answer these in order to reach a final net ionic reaction:


What are the ions that are present in the final product (ammonium oxalate)?



   The ions involved are ammonium ($\ce{NH4+}$) and oxalate ($\ce{C2O4^{2-}}$).



Notice the charges of those ions:



   Ammonium has a 1+ charge (that's written correctly as +, but of course, I wanted to emphasize) and oxalate has a 2-.



The other ions are spectator ions. These two ions actually form the precipitate. But the final formula (where your misunderstanding rises from) is



   $\ce{(NH4)2C2O4}$


You can now write the net ionic equation and get it balanced.