Here's why:

* Ionic Compound: BaO is an ionic compound formed by the strong electrostatic attraction between barium cations (Ba²⁺) and oxide anions (O²⁻).

* High Melting Point: Ionic compounds generally have high melting points due to the strong bonds between the ions. BaO has a very high melting point of 1923°C (3493°F).

* Room Temperature: Room temperature is significantly lower than BaO's melting point, so it exists as a solid at room temperature.