Answer:
Atomic number
Step-by-step explanation:
The number of protons in an atom is equal to the atomic number of the atom.
The mass number of an element is defined as the sum of number of protons and neutrons.
The atomic number of an element is defined as the number of protons in the nucleus of the atom.
The atomic number is generally represented by letter Z.
The mass number is generally represented by the letter A.