The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of an atom.
 It is identical to the charge number of the nucleus.
 The atomic number uniquely identifies a chemical element.
 In an uncharged atom, the atomic number is also equal to the number of electrons.
Oxygen is a chemical element with symbol O and atomic number 8.
 It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds.
 By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium.
 At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2 .
 Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere.
 As compounds including oxides, the element makes up almost half of the Earth's crust.
Unbinilium, also known as eka-radium or simply element 120, is the hypothetical chemical element in the periodic table with symbol Ubn and atomic number 120.
 "Unbinilium" and "Ubn" are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon.
 In the periodic table of the elements, it is expected to be an s-block element, an alkaline earth metal, and the second element in the eighth period.
 It has attracted attention because of some predictions that it may be in the island of stability, although newer calculations expect the island to actually occur at a slightly lower atomic number, closer to copernicium and flerovium.
Unbiunium, also known as eka-actinium or element 121, is the hypothetical chemical element with symbol Ubu and atomic number 121.
 "Unbiunium" and "Ubu" are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon.
 In the periodic table of the elements, it is expected to be the first of the superactinides, and the third element in the eighth period: analogously to lanthanum and actinium, it could be considered the fifth member of group 3 and the first member of the fifth-row transition metals.
 It has attracted attention because of some predictions that it may be in the island of stability, although newer calculations expect the island to actually occur at a slightly lower atomic number, closer to copernicium and flerovium.
Moseley's law is an empirical law concerning the characteristic x-rays that are emitted by atoms.
 The law was discovered and published by the English physicist Henry Moseley in 1913.
 It is historically important in quantitatively justifying the conception of the nuclear model of the atom, with all, or nearly all, positive charges of the atom located in the nucleus, and associated on an integer basis with atomic number.
 Until Moseley's work, "atomic number" was merely an element's place in the periodic table, and was not known to be associated with any measureable physical quantity.
 Moseley was able to show that the frequencies of certain characteristic X-rays emitted from chemical elements are proportional to the square of a number which was close to the element's atomic number; a finding which supported Van den Broek and Bohr's model of the atom in which the atomic number is the same as the number of positive charges in the nucleus of the atom.
 In brief, the law states that the square root of the frequency of the emitted x-ray is proportional to the atomic number.
Polonium is a chemical element with symbol Po and atomic number 84.
 A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth.
 Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238.
 Though slightly longer-lived isotopes exist, they are much more difficult to produce.
 Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth.
 Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.
The mass number (symbol "A"), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.
 It determines the atomic mass of atoms. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion.
 The mass number is different for each different isotope of a chemical element.
 This is not the same as the atomic number ("Z") which denotes the number of protons in a nucleus, and thus uniquely identifies an element.
 Hence, the difference between the mass number and the atomic number gives the number of neutrons ("N") in a given nucleus: "N=A−Z".
Nobelium is a synthetic chemical element with symbol No and atomic number 102.
 It is named in honor of Alfred Nobel, the inventor of dynamite and benefactor of science.
 A radioactive metal, it is the tenth transuranic element and is the penultimate member of the actinide series.
 Like all elements with atomic number over 100, nobelium can only be produced in particle accelerators by bombarding lighter elements with charged particles.
 A total of twelve nobelium isotopes are known to exist; the most stable is No with a half-life of 58 minutes, but the shorter-lived No (half-life 3.1 minutes) is most commonly used in chemistry because it can be produced on a larger scale.
Lawrencium is a synthetic chemical element with symbol Lr (formerly Lw) and atomic number 103.
 It is named in honor of Ernest Lawrence, inventor of the cyclotron, a device that was used to discover many artificial radioactive elements.
 A radioactive metal, lawrencium is the eleventh transuranic element and is also the final member of the actinide series.
 Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles.
 Twelve isotopes of lawrencium are currently known; the most stable is Lr with a half-life of 11 hours, but the shorter-lived Lr (half-life 2.7 minutes) is most commonly used in chemistry because it can be produced on a larger scale.
Chalcogenide glass (hard "ch" as in "chemistry") is a glass containing one or more chalcogens (sulfur, selenium and tellurium, but excluding oxygen).
 Such glasses are covalently bonded materials and may be classified as covalent network solids. Polonium is also a chalcogen but is not used because of its strong radioactivity.
 Chalcogenide materials behave rather differently from oxides, in particular their lower band gaps contribute to very dissimilar optical and electrical properties.

Question: What is the atomic number for the chemical element which is also a radioactve chalcogen?
Answer: 84