Which of the following is formed by joining two or more different atoms together?

• A. A compound
• B. A molecule of oxygen (O_2)
• C. An element
• D. A mixture

Answer: (A)

Verified step by step guidance

1. Understand the definitions of the terms involved: An element is a pure substance consisting of only one type of atom; a molecule is two or more atoms bonded together, which can be the same or different atoms; a compound is a molecule that contains at least two different types of atoms chemically bonded; a mixture is a physical combination of two or more substances that are not chemically bonded.
2. Analyze the example given: A molecule of oxygen (O_2) consists of two oxygen atoms bonded together, but since both atoms are the same element, it is not a compound but a molecule of an element.
3. Recognize that a compound must have atoms of different elements chemically bonded, such as H_2O (water), which contains hydrogen and oxygen atoms.
4. Conclude that the correct answer is a compound because it specifically refers to a substance formed by joining two or more different atoms together chemically.
5. Remember that mixtures are not chemically bonded substances, so they do not fit the description of being formed by joining atoms together.