Final answer:
The smallest particle of an element that retains its characteristics is an atom, which is composed of subatomic particles including protons, neutrons, and electrons.
Step-by-step explanation:
The smallest particle of an element that retains the characteristics of the element is an atom. Atoms are composed of smaller parts known as subatomic particles which include protons, neutrons, and electrons. The atomic structure is crucial because it determines the properties and behaviour of an element. The atomic number of an element, which defines its identity, is the number of protons found in the nucleus of its atoms.