Calcium oxide, sometimes known as quicklime, is a chemical substance with the formula CaO. It is a white, crystalline solid at room temperature and is widely utilized in various industries due to its versatile properties. Calcium oxide is composed of one calcium (Ca) atom and one oxygen (O) atom, forming a simple and stable ionic compound. At room temperature, calcium oxide exists as a white, odorless solid with a high melting point. Quicklime is highly reactive with water, producing heat in an exothermic reaction. This property is exploited in various applications, including its use in traditional lime kilns.