* Metal and Nonmetal: Iron (Fe) is a metal, and oxygen (O) is a nonmetal. This combination is a strong indicator of ionic bonding.

* Electron Transfer: Iron readily loses two electrons to form a Fe²⁺ cation. Oxygen, being highly electronegative, gains two electrons to form an O²⁻ anion. The electrostatic attraction between these oppositely charged ions constitutes the ionic bond.

Important Note: While FeO is predominantly ionic, it can exhibit some covalent character due to the high electronegativity of oxygen. However, the ionic nature is more dominant.