Why is water (H_2O) not listed as an element on the periodic table?

• A. Because water is a compound made of hydrogen and oxygen elements.
• B. Because water is a mixture, not a pure substance.
• C. Because water is a noble gas and noble gases are not shown on the periodic table.
• D. Because water is an isotope of hydrogen.

Answer: (A)

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, characterized by its atomic number (number of protons).
2. Recognize that water (H_2O) is composed of two different elements, hydrogen and oxygen, chemically bonded together in a fixed ratio.
3. Recall that the periodic table lists only elements, not compounds or mixtures, so substances made of multiple elements bonded together are not listed as individual entries.
4. Identify that water is a compound, not a mixture or an isotope, and it is certainly not a noble gas, so those options are incorrect.
5. Conclude that water is not listed on the periodic table because it is a compound made from hydrogen and oxygen elements, not a single element itself.