An atom's element type is determined by which of the following?

The element type of an atom is determined by the number of protons it contains within its nucleus. This number is referred to as the atomic number, and each element on the periodic table is uniquely identified by its atomic number. For example, hydrogen has one proton, so its atomic number is 1, making it hydrogen; whereas carbon has six protons, so its atomic number is 6, identifying it as carbon.

While neutrons and electrons contribute to the properties of an atom, they do not determine the element itself. The number of neutrons can vary among different isotopes of the same element, which affects the atomic mass but not the elemental identity. Electrons are responsible for chemical bonding and the electrical charge of the atom but do not change the fundamental identity of the element, which is defined solely by the proton count. The number of isotopes, which reflects variations in neutron count, does not influence what element the atom represents. Therefore, the number of protons is the defining characteristic of the element type.