Which of the following elements is NOT commonly found in organic molecules?

Organic molecules are primarily composed of carbon atoms, which form the backbone of these molecules. Alongside carbon, other elements such as hydrogen, oxygen, nitrogen, sulfur, and phosphorous are often present, playing critical roles in the structure and function of organic compounds.

Helium, however, is a noble gas and does not participate in chemical bonding to form stable compounds. It is rarely found in organic molecules because it lacks the ability to form bonds with carbon or other elements. In contrast, carbon, oxygen, and nitrogen are essential elements in the composition of a wide variety of organic compounds, including carbohydrates, proteins, lipids, and nucleic acids.

This distinction helps clarify why helium is not commonly associated with organic chemistry, making it the correct answer.