Concept:Carbon (IV) oxide is detected by its reaction with lime water, which turns milky.Explanation:Lime water is a dilute solution of calcium hydroxide, Ca(OH)2.When carbon (IV) oxide gas is bubbled through it, a white insoluble solid called calcium carbonate forms.The chemical equation is:CO2+Ca(OH)2→CaCO3↓+H2OThe milky appearance of the solution confirms the presence of carbon (IV) oxide.Answer:B. lime water