a. Marble is chemically composed of calcium carbonate (CaCO3). According to the question, the student dropped few pieces of marble in dilute HCl contained in a test tube. We know that acids react with calcium carbonate to form or give the corresponding salt, carbon dioxide and water. Hence, when we pass the carbon dioxide gas through lime water a white precipitate would be observed to form in the test tube containing the lime water.
b. The balanced chemical equation for the above change when we pass the carbon dioxide gas through lime water is: -
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
