Question

which statement below best explains what happened?
compounds are broken down into the same elements from which they are made.
atoms of different elements combine to form other elements
atoms of different elements combine to form compounds.
compounds combine to form different elements.

Explanation:

The first two boxes show separate atoms (left - box) and molecules of an element (middle - box). The third box shows a compound formed by the combination of atoms from the first two boxes. Compounds are formed when atoms of different elements combine. Elements are pure substances and atoms of different elements do not combine to form other elements (as elements are defined by their atomic number). Also, the starting materials are not compounds (the left - box has atoms of an element and the middle - box has molecules of an element), so the process is not about breaking down compounds. And compounds do not combine to form elements in this case.

Answer:

Atoms of different elements combine to form compounds.