Final answer:
The compound that is not an ionic compound is PCl5.
Step-by-step explanation:
The correct answer is (a) PCl5. This is because PCl5 is a covalent compound, not an ionic compound. Ionic compounds are formed when a metal and a non-metal combine, resulting in the transfer of electrons. Covalent compounds, on the other hand, are formed when two non-metals share electrons. In the case of PCl5, both phosphorus (P) and chlorine (Cl) are non-metals, so they share electrons to form covalent bonds.