Concept:Quicklime is the common name for calcium oxide, which has the chemical formula CaO.Explanation:Calcium oxide is prepared by heating limestone (calcium carbonate) strongly. It is a white, caustic, and alkaline solid at room temperature. It is also known as burnt lime. Among the given options, CaCO₂ is not a correct formula, Ca(OH)₂ is slaked lime, and CaCl₂ is calcium chloride. Only CaO corresponds to quicklime.Answer:D. CaO