Final answer:
The compound most likely to be covalent is CaSO4.
Step-by-step explanation:
Out of the given compounds, the most likely to be covalent is option E: CaSO4. Covalent compounds are formed when nonmetals bond with each other. In CaSO4, calcium (Ca) is a metal and sulfate (SO4) is a polyatomic ion. Polyatomic ions, like sulfate, are formed by the combination of nonmetals and metals. Therefore, CaSO4 is an ionic compound, not covalent.
Similarly, options A, B, C, and D are also ionic compounds. Potassium fluoride (KF), calcium chloride (CaCl2), aluminum oxide (Al2O3), and chlorine dioxide (ClO2) all contain metals bonded with nonmetals, making them ionic.
To summarize, the compound most likely to be covalent is option E: CaSO4.