Final answer:
Ionic compounds are arranged by expected melting points from lowest to highest as CsBr, RbF, SrF2, and SrO, based on ion charges and sizes.
Step-by-step explanation:
The strength of an ionic bond is influenced by the charges of the ions and their sizes. Higher charges lead to stronger attractions, and smaller ion sizes allow ions to get closer, thus strengthening the bond. Therefore, when arranging ionic compounds by expected melting points based on ion charges and relative sizes, we must consider both factors. As a larger ion with a 1+ charge, CsBr will likely have the lowest melting point. RbF, with a 1+ charge but smaller ions than CsBr, should have a higher melting point. SrO and SrF2 both have a 2+ charge on the strontium ion, but oxygen is smaller than fluoride, so SrO likely has an even stronger bond and a higher melting point than SrF2. Hence, the order from lowest to highest expected melting point is CsBr, RbF, SrF2, and SrO.