Answer :
A solution of slaked lime is used for whitewashing walls because Calcium hydroxide(slaked lime) reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of whitewashing and gives a shiny finish to the walls. \( Ca{(OH)}_{2}{(aq)} +CO_{2}{(g)} \rightarrow CaCO_{3}{(s)}+H_{2}O_{(l)} \)