Isotopes
Elements having same atomic number Z, but different A mass number for example 126C, 146C and 11H 21H, 31H are isotopes of carbon and hydrogen.
Isotones
Elements having same number of neutrons (N) but different atomic number for example (Z) 42He, 31H.
Isobars
elements having same mass number (A) but different atomic number (Z) are called isobars, for example, 146C 147C are isobars. Protons and neutrons together are called nucleons.