Here's how you can figure that out:

* Caesium (Cs) is in group 1 of the periodic table, meaning it has a +1 charge as an ion.

* Sulfate (SO₄) is a polyatomic ion with a -2 charge.

To balance the charges, you need two caesium ions (+1 each) to balance the -2 charge of the sulfate ion. This gives you the formula Cs₂SO₄.