Which ionic compound is commonly used as a building material (e.g., in limestone, marble, and cement)?

• A. Potassium nitrate, $KN{O}_3$
• B. Ammonium sulfate, $N_1{H}_4{S}_1{O}_4$
• C. Sodium chloride, $NaCl$
• D. Calcium carbonate, $C_{1}a{C}_1{O}_3$

Answer: (D)