Final answer:
Carbon is the element that can form chains, bond with other elements, and create complex structures, making it essential for life. The answer is option D.
Step-by-step explanation:
The element that can form chains of itself, bond with other elements, and form complex structures is Carbon (D). Carbon's unique ability to form stable covalent bonds with itself and with other elements allows for a multitude of molecular variations.
These molecules can have various forms, including long chains, branching structures, and rings with the potential to connect with other rings. This versatility explains why carbon is the backbone of all known life, as it forms the complex molecules that determine the structures and functions of living systems.