Which of the following statements concerning molecules and compounds is true?

• A. Compounds consist of only one type of atom.
• B. All molecules are compounds, and all compounds are molecules.
• C. Molecules cannot be formed from two atoms of the same element.
• D. All compounds are molecules, but not all molecules are compounds.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the definitions of key terms: A molecule is two or more atoms bonded together, which can be of the same or different elements. A compound is a substance formed when two or more different elements are chemically bonded together.
2. Step 2: Analyze the statement 'Compounds consist of only one type of atom.' Since compounds must have at least two different elements, this statement is false.
3. Step 3: Analyze the statement 'All molecules are compounds, and all compounds are molecules.' Since molecules can be made of the same element (like O\_2) and compounds require different elements, this statement is false.
4. Step 4: Analyze the statement 'Molecules cannot be formed from two atoms of the same element.' Since molecules like O\_2 and N\_2 exist, this statement is false.
5. Step 5: Understand why 'All compounds are molecules, but not all molecules are compounds' is true: Compounds are molecules with different elements, but molecules can also be made of the same element, so this statement correctly distinguishes the relationship.