How to determine the number of electrons, protons and neutrons in an atom ?

From the knowledge of atomic number (Z) and mass number (A) of an element, one can determine the number of electrons, protons and neutrons in an atom of that element as follows. For an atom, were know,

No. of electrons= No. of protons (P)

But, No. of protons (P) = Atomic number (Z)

So, for an atom,

No. of electrons = Atomic number (Z)

We also know that,

Mass number (A) = No. of protons (P) + No. of neutrons (N) = Atomic number (Z) + number of neutrons (Z)

No. of neutrons (N) = Mass number (A) – Atomic number (Z)