UPSC NDA 2 2021 General Ability Solved Paper

White colour precipitate is obtained by passing CO2 (carbon dioxide) gas through lime water. Carbon dioxide reacts with limewater (a solution of calcium hydroxide, Ca(OH)2, to form a white precipitate (appears milky) of calcium carbonate, CaCO3. Adding more carbon dioxide results in the precipitate dissolving to form a colourless solution of calcium hydrogencarbonate.