Answer:
B
Step-by-step explanation:
B is the correct answer. A molecule is made up of at least two atoms, but not nessessarily with the same element. A compound is made up of two or more atoms AND there are at least two different elements. Therefore, a molecule can be a compound if it has two different elements, or a chemical substance if it has only one type of element.
* By the way, elements are from the Periodic Table
Or you can use the process of elimination to rule out A, C, and D, if it's too confusing. C is not true because not all elements exists as molecules. They exist as atoms. D is not true because when two atoms combine, they always form a molecule, not a compound. A is not true because a compound IS a molecule, while a molecule CAN BE a compound.