Stability Criterion
A survey of periodic table carefully reveals that those elements in which N / Z = 1 or 1.6 are stable. Amongst these, the elements having even N and even Z are the most stable and are termed as magic numbers.
The heaviest stable nuclide is 2009Bi83. Lend (2008pb82) is the most stable heaviest element. All transuranic elements finally disintegrate into lead (Pb). The elements or nuclides which decay with time are termed as radioactive nuclides.
The element / nuclide, whose binding energy per nucleon is less than 7.5 MeV, are (mostly) unstable.