Here's how to predict the formula for the compound formed between potassium (K) and sulfur (S):

* Identify the charges:

* 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⁻).

* Balance the charges: To create a neutral compound, you need two potassium ions (2 x +1 = +2) to balance the charge of one sulfide ion (-2).

* Write the formula: The formula for the compound is K₂S.