Here's how we arrive at this:

* Ruthenium(III) indicates that ruthenium has a +3 charge (Ru³⁺).

* Sulfate is a polyatomic ion with a -2 charge (SO₄²⁻).

To balance the charges, we need two ruthenium ions (2 x +3 = +6) and three sulfate ions (3 x -2 = -6).