DescriptionNucleonic symmetry of the most abundant isotopes.png
English: The first 16 elements (out of 82 known elements) comprise 99.9% of the matter of the universe. Aside from hydrogen, all the most abundant isotopes have an equal number of protons and neutrons.
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Captions
Isotopes shown here comprise 99.9% of the ordinary matter of the universe, and isotopes in boxes have symmetry (equality) in numbers of protons and neutrons.