The correct answer is Calcium hydrogen carbonate.Concept:Chemical reaction:It is a process in which one or more substances, the reactants, are converted to one or more different substances, the products.A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.Double displacement reaction: It is a chemical reaction in which two compounds react and exchange their ions forming new products. This reaction often results in the formation of an insoluble compound called a precipitate. Such reactions are represented by equations of the following form: A+B- + C+D- ? A+D- + B-C+?Explanation:When carbon dioxide gas is passed through lime water or calcium hydroxide, double displacement takes place and a white precipitate of calcium carbonate is formed.The chemical equation for the above reaction is as follows: Ca(OH)2(aq) + CO2 (g) ? CaCO3(s) + H2O(l)The calcium carbonate formed is a precipitate and it is not soluble in water. It gives a milky appearance to the solution. When an excess of carbon dioxide gas is passed through the solution, the following reaction takes place: CaCO3(s) + H2O(l) + CO2(g) ? Ca(HCO3)2In the above chemical reaction, the product formed is calcium bicarbonate or calcium hydrogen carbonate which is soluble in water. ?