CaO, also known as calcium oxide, is an ionic compound. Ionic compounds are formed when a metal and a non-metal combine through the transfer of electrons. In the case of CaO, calcium (a metal) donates two electrons to oxygen (a non-metal), resulting in the formation of an ionic bond. Ionic compounds typically have high melting and boiling points, and they conduct electricity when dissolved in water. Therefore, based on the properties and composition of CaO, it can be concluded that it is an ionic compound.