Final answer:
The electron plays the greatest role in determining the physical and chemical properties of an element.
Step-by-step explanation:
The subatomic particle that plays the greatest role in determining the physical and chemical properties of an element is the electron.
Electrons are negatively charged particles that orbit the nucleus of an atom. They determine the overall charge of the atom and are responsible for chemical reactions and bonding.
For example, the number and arrangement of electrons in an atom's outer shell determine its chemical reactivity. Elements with a full outer shell of electrons, like noble gases, are stable and less likely to react with other elements.
Learn more about role of electrons in determining element properties