In which pair do both compounds exhibit predominantly ionic bonding?

Question

Quizplus · Accepted Answer

Ionic bonding occurs between a metal and a non-metal. KI and O₃ have covalent character due to the high electronegativity difference between O and S, and PCl₅ and HCl have covalent character due to the small electronegativity difference between P or Cl and H. NaF and H₂O have covalent character due to the electronegativity difference between H and F being too small to form an ionic bond. NaCl and CaO both have a metal (Na, Ca) and non-metal (Cl, O) combination, with a large electronegativity difference, so they exhibit predominantly ionic bonding. Na₂SO₄ and BF₃ have covalent character due to the small electronegativity difference between the elements.

In Which Pair Do Both Compounds Exhibit Predominantly Ionic Bonding