Which one of the following is considered as the basic structural element of all life forms?

Carbon is considered the basic structural element of all life forms on Earth. It serves as the fundamental building block for all organic macromolecules, including carbohydrates, lipids, proteins, and nucleic acids (DNA and RNA).

The primary reason for carbon's central role is its tetravalency; it can form four stable covalent bonds with other atoms, including other carbon atoms. This allows for the creation of complex, stable, and diverse molecular structures such as long chains and rings (a property known as catenation). While elements like Oxygen, Nitrogen, and Phosphorus are essential components of living organisms (often grouped together as CHNOPS), they generally serve as functional groups or links attached to the primary carbon backbone rather than forming the structural framework itself.