Answer:
Atomic number, mass number.
Explanation:
The three sub atomic particles of the atoms are electron, proton and neutron. The atomic number of the element is equal to the number of protons of the element.
Isotopes may be defined as the elements that have the same atomic but different mass number. The simplest example of isotopes are protium, deuterium and tritium. They have the same atomic number 1. These are the isotopes of hydrogen.
Thus, the correct answer is option (A).
