Chemistry: The Central Science (13th Edition)

$K_2(SO_4)$
Potassium is an alkali metal, so it has a charge of 1+. The Sulfate ion, which has a chemical formula of $(SO_4)2-$, has a charge of 2-. Since the magnitude of the sulfate charge is twice as great as the magnitude of the Potassium charge, there must be two Potassium atoms for every one Sulfate ion to create a balanced charge. Thus, the chemical formula for Potassium Sulfate is $K_2(SO_4)$.