The ionic compound formed by potassium (K) and sulfur (S) is potassium sulfide, with the chemical formula K₂S.

Here's how to determine the formula:

* Potassium is in group 1 of the periodic table, so it forms a +1 ion (K⁺).

* Sulfur is in group 16, so it forms a -2 ion (S²⁻).

* To balance the charges, you need two potassium ions (2 x +1 = +2) to combine with one sulfide ion (-2).

Therefore, the formula for potassium sulfide is K₂S.