Is $$CaO$$ an alkali or a base?
$$CaO$$ is a basic oxide, as it follows the general rule that Metal oxides are basic, non-metal oxides are acidic.
Now, we need to check if it's soluble or not as if it is soluble, it's considered an alkali, but if it's insoluble, it is a base.
$$CaO$$ is slightly soluble, so it is considered to be alkali.
Calcium oxide $$(CaO)$$, commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature.