Which of the following is an example of an element?

• A. Carbon dioxide (CO_2)
• B. Water (H_2O)
• C. Oxygen (O)
• D. Sodium chloride (NaCl)

Answer: (C)

Verified step by step guidance

1. Understand the definition of an element: An element is a pure substance consisting of only one type of atom, represented by a unique chemical symbol on the periodic table.
2. Analyze each option to determine if it is an element or a compound: Compounds are substances made of two or more different elements chemically bonded together.
3. Look at Carbon dioxide (CO_2): It contains carbon and oxygen atoms bonded together, so it is a compound, not an element.
4. Look at Water (H_2O): It contains hydrogen and oxygen atoms bonded together, so it is a compound, not an element.
5. Look at Oxygen (O): It consists of only oxygen atoms and is represented by the symbol 'O' on the periodic table, so it is an element.