Answer;
4) CaO and MgO
Explanation;
-Both CaO and MgO are compounds .
-Compounds are substances that are formed when two or more chemical elements are chemically bonded together. CaO is formed when Calcium and oxygen atom chemically combine while MgO is formed when magnesium atom and oxygen atom chemically combines.
-While elements can not be broken down (decomposed) into simpler substances by chemical means, compounds can be broken down into simpler substances chemically (into constituent atoms).
