Why is the effect of carbonation clearly seen on limestone?

Correct answer: Because limestone can dissolve easily

Direct answer: A is correct. Carbonation is a chemical weathering process involving carbon dioxide and water. Carbon dioxide dissolves in rainwater or soil water and forms weak carbonic acid, represented simply as carbon dioxide plus water forming carbonic acid. This weak acid reacts readily with calcium carbonate, the main mineral in limestone, and can dissolve it, especially where water moves through cracks and joints. Repeated dissolution may create caves, sinkholes and other karst features. Option A is correct because limestone is comparatively soluble in weak carbonic acid. Option B is wrong because limestone does react chemically. Option C is wrong because limestone is not made only of sand; it is mainly calcium carbonate, often formed from shells or other carbonate material. Option D is wrong because constant heat is not the essential cause of carbonation. Memory cue: carbon dioxide plus water attacks calcium carbonate, so carbonation strongly affects limestone.