The electrostatic attraction between oppositely charged ions.

Here's why:

* Ions: Ionic bonds form between atoms that have gained or lost electrons, resulting in charged particles called ions.

* Opposite Charges: Positively charged ions (cations) are attracted to negatively charged ions (anions).

* Electrostatic Attraction: This attraction between opposite charges is the force that holds the ions together in an ionic compound.

In simpler terms:

Imagine magnets with opposite poles attracting each other. That's essentially what happens in an ionic bond. One atom gives up an electron, becoming positively charged, while another atom gains that electron, becoming negatively charged. These opposite charges then "stick" together, forming a strong bond.