UPSC CDS 1 2021 GK Paper

This slaked lime reacts with CO2 in the air to form a thin layer of CaCO3 to give a shiny finish. The calcium oxide (CaO) is also called quicklime. It is used for whitewashing by producing calcium hydroxide (CaOH). Calcium hydroxide reacts with water and absorbs carbon dioxide (CO2) from the environment. Then it produces calcium carbonate (CaCO2) which creates a shiny finish on the walls.