With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Carbon has 6 as its atomic number.
text_B: Carbon -LRB- from carbo `` coal '' -RRB- is a chemical element with symbol C and atomic number 6 .. chemical element. chemical element. symbol. Symbol ( chemistry ). atomic number. atomic number. coal. coal. It is nonmetallic and tetravalent -- making four electrons available to form covalent chemical bonds .. tetravalent. tetravalence. covalent. covalent bond. Three isotopes occur naturally , C and C being stable , while C is a radioactive isotope , decaying with a half-life of about 5,730 years .. isotopes. Isotopes of carbon. radioactive isotope. Radionuclide. half-life. half-life. Carbon is one of the few elements known since antiquity .. few elements known since antiquity. Discoveries of the chemical elements. Carbon is the 15th most abundant element in the Earth 's crust , and the fourth most abundant element in the universe by mass after hydrogen , helium , and oxygen .. fourth most abundant element in the universe by mass. Abundance of the chemical elements. hydrogen. hydrogen. helium. helium. oxygen. oxygen. Earth. Earth. Carbon 's abundance , its unique diversity of organic compounds , and its unusual ability to form polymers at the temperatures commonly encountered on Earth enables this element to serve as a common element of all known life .. Earth. Earth. all known life. Carbon-based life. compounds. chemical compound. It is the second most abundant element in the human body by mass -LRB- about 18.5 % -RRB- after oxygen .. oxygen. oxygen. human body. human body. The atoms of carbon can bond together in different ways , termed allotropes of carbon .. allotropes of carbon. allotropes of carbon. The best known are graphite , diamond , and amorphous carbon .. graphite. graphite. diamond. diamond. amorphous carbon. amorphous carbon. The physical properties of carbon vary widely with the allotropic form .. physical properties. physical properties. For example , graphite is opaque and black while diamond is highly transparent .. graphite. graphite. diamond. diamond. opaque. Opacity ( optics ). transparent. Transparency ( optics ). Graphite is soft enough to form a streak on paper -LRB- hence its name , from the Greek verb '' γραφειν '' which means `` to write '' -RRB- , while diamond is the hardest naturally occurring material known .. diamond. diamond. Graphite is a good electrical conductor while diamond has a low electrical conductivity .. diamond. diamond. electrical conductor. electrical conductor. electrical conductivity. electrical conductivity. Under normal conditions , diamond , carbon nanotubes , and graphene have the highest thermal conductivities of all known materials .. diamond. diamond. graphene. graphene. thermal conductivities. thermal conductivity. all known materials. List of thermal conductivities. All carbon allotropes are solids under normal conditions , with graphite being the most thermodynamically stable form .. graphite. graphite. thermodynamically stable. Thermodynamic equilibrium. They are chemically resistant and require high temperature to react even with oxygen .. oxygen. oxygen. The most common oxidation state of carbon in inorganic compounds is +4 , while +2 is found in carbon monoxide and transition metal carbonyl complexes .. oxidation state. oxidation state. carbon monoxide. carbon monoxide. transition metal. transition metal. carbonyl. Metal carbonyl. compounds. chemical compound. The largest sources of inorganic carbon are limestones , dolomites and carbon dioxide , but significant quantities occur in organic deposits of coal , peat , oil , and methane clathrates .. carbon dioxide. carbon dioxide. coal. coal. peat. peat. oil. petroleum. Carbon forms a vast number of compounds , more than any other element , with almost ten million compounds described to date , and yet that number is but a fraction of the number of theoretically possible compounds under standard conditions .. compounds. chemical compound. For this reason , carbon has often been referred to as the `` king of the elements '' .
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