Atomic number:

The atomic number of an element is defined as the total number of protons present in the nucleus of an atom. It is equal to the number of electrons present in the atom. It is represented by the letter Z.

Mass Number:

It is defined as the total number of protons and neutrons present in the nucleus of an atom of an element. It is represented by the letter A.

Thus Atomic Number Z= Number of protons = Number of electrons Mass Number A = Number of protons + Number of Neutrons