Oppositely charged ions in an ionic compound are held together by electrostatic forces. These forces are the attractions between the positive and negative ions, which form the ionic bonds that hold the compound's lattice together. The strength of these ionic bonds depends on the magnitude of the charges on the ions and the distance between them, according to Coulomb's law. This strong electrostatic attraction is why ionic compounds have high melting and boiling points and form crystalline structures.
So, the sentence should be filled as:
"Oppositely charged ions in an ionic compound are held together by
electrostatic forces."
