Here's how to determine the total number of atoms in one formula unit of ammonium oxalate (NH₄₂C₂O₄):

* Break down the formula:

* NH₄: Ammonium ion (NH₄⁺)

* ₂: There are two ammonium ions.

* C₂O₄: Oxalate ion (C₂O₄²⁻)

* Count the atoms:

* Nitrogen (N): 2 (from the two ammonium ions)

* Hydrogen (H): 8 (2 ammonium ions x 4 hydrogen atoms per ammonium ion)

* Carbon (C): 2

* Oxygen (O): 4

* Total: 2 + 8 + 2 + 4 = 16 atoms

Therefore, there are 16 total atoms in one formula unit of ammonium oxalate (NH₄₂C₂O₄).