Isotopes are atoms of the same element (rather elements) having same atomic number (Z), but different mass number (A) (rather atomic mass). Isotopes differ from each other with respect to number of neutrons.
Almost all elements have isotopes.
Isobars: Atoms of different elements with different atomic number but with the same mass number are called isobars. For example calcium and argon have different number of electrons and have different atomic numbers. But they have same mass number as 40 and so they are said to be isobars.
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