What is the criss cross rule?

The criss-cross rule is a method used in chemistry to determine the formula of ionic compounds. It involves taking the charge of one ion and using it as the subscript for the other ion, effectively "criss-crossing" the charges. For example, if you have a sodium ion (Na⁺) and a chloride ion (Cl⁻), the formula would be Na₁Cl₁, which simplifies to NaCl. This rule ensures that the resulting compound is electrically neutral.