Final answer:
The number of protons in an element's atom is equal to its atomic number, which is a defining characteristic of the element.
Step-by-step explanation:
The statement that describes the number of protons in each atom of an element is C) The number of protons is equal to the atomic number. The atomic number (Z) uniquely defines an element and represents the number of protons in its nucleus. It is also equivalent to the number of electrons in a neutral atom, ensuring electrical neutrality.
Isotopes of an element have the same number of protons but different numbers of neutrons. The total number of protons and neutrons is known as the mass number (A), not to be confused with atomic mass. To calculate the number of neutrons in an atom, subtract the atomic number from the mass number: A - Z = number of neutrons.