Here's how to determine the chemical formula for nickel(III) oxalate:

* Nickel(III) ion: The Roman numeral III indicates that nickel has a +3 charge (Ni³⁺).

* Oxalate ion: The oxalate ion has a -2 charge (C₂O₄²⁻).

To balance the charges, we need two nickel(III) ions and three oxalate ions:

* 2 Ni³⁺ + 3 C₂O₄²⁻ → Ni₂(C₂O₄)₃

Therefore, the chemical formula for nickel(III) oxalate is Ni₂(C₂O₄)₃.