Final answer:
Protons determine the identity of an element and contribute to its mass.
Step-by-step explanation:
The role of a proton in the atom is that it determines the identity, or what element an atom is. The number of protons in the nucleus of an atom is its atomic number, which is unique for each element. For example, any atom with six protons is carbon, regardless of the number of neutrons or electrons it may have. Additionally, the number of protons contributes to an element's mass, as protons and neutrons make up nearly all of an atom's mass. Hence, protons function not only as elemental identifiers but also as contributors to an element's mass, showcasing their fundamental significance within atomic structure and classification.