When a potassium ion (K⁺) combines with a sulfide ion (S²⁻), the charges of the ions must balance to form a neutral compound. The potassium ion has a charge of +1, while the sulfide ion has a charge of -2.
To balance the charges, you would need two potassium ions to pair with one sulfide ion. The formula for the compound formed is therefore:
\[ \text{K}_2\text{S} \]
This means that the compound is potassium sulfide.