Here's how to write the formula for nickel(III) sulfate:

1. Identify the Ions:

* Nickel(III): This tells us the nickel ion has a +3 charge (Ni³⁺).

* Sulfate: This is the polyatomic ion SO₄²⁻.

2. Balance the Charges:

* To balance the charges, we need two Ni³⁺ ions to balance three SO₄²⁻ ions.

3. Write the Formula:

* The formula for nickel(III) sulfate is Ni₂(SO₄)₃.