How do atoms with stable nuclei differ from atoms with unstable nuclei?

A stable atom is an atom that has enough binding energy to hold the nucleus together permanently. An unstable atom does not have enough binding energy to hold the nucleus together permanently and is called a radioactive atom.

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in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

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