The correct formula unit for the ionic compound strontium chloride consists of 1 Sr²⁺ ion and 2 Cl⁻ ions.
Strontium has a 2+ charge (Sr²⁺), and chloride has a 1- charge (Cl⁻). To balance the charges in the compound, you need two chloride ions for every strontium ion, which results in the formula SrCl₂.
So the answer is: 1 Sr²⁺ ion and 2 Cl⁻ ions.