Which of the following best defines an element?

An element is defined as a substance that cannot be broken down into simpler substances through chemical means. This fundamental definition emphasizes the basic nature of elements as the building blocks of matter. Each element is composed of atoms that have the same number of protons in their nuclei, which distinguishes one element from another.

In contrast to other types of substances, such as compounds and mixtures, elements cannot be simplified or decomposed into more basic substances without undergoing a chemical transformation that fundamentally alters their identity. Therefore, elements hold a unique position in the hierarchy of matter, and understanding this definition is essential for grasping key concepts in chemistry, including the periodic table, atomic structure, and chemical bonding.

The other options involve concepts that are related to elements and compounds but do not accurately capture their defining characteristic. Understanding this distinction is crucial for a solid foundation in chemistry.