The formula for copper(II) oxalate is CuC₂O₄. Here's how we arrive at that:

* Copper(II): This tells us the copper ion has a +2 charge (Cu²⁺).

* Oxalate: This is the polyatomic ion C₂O₄²⁻, with a -2 charge.

Since the charges are equal and opposite, the formula needs one copper ion and one oxalate ion, resulting in CuC₂O₄.