The class of matter in which there are 106 different varieties-?

Most physical and chemical characteristics of a substance relate to the nuclei's neutron-proton composition. The number of protons in a nucleus is the atomic number (Z) and establishes the chemical identity of the atom. Each atomic number corresponds to a different chemical element; there are now approximately 106 known chemical elements that correspond to nuclei containing from 1 to 106 protons.