B. Chemical button 18 mm.

<div>   </div> <div> <strong> Atomic number <span class = "Apple-tab-span" style = "white-space: pre;"> </span>   5 </strong> </div> <div> <strong> Atomic mass   <span class = "Apple-tab-span" style = "white-space: pre;"> </span>10,811</strong></div> <div> <strong> Density, kg / m3? <span class = "Apple-tab-span" style = "white-space: pre;"> </span>   2340 </strong> </div> <div> <strong> Temperature</strong></div> <div> <strong> melting, ° С       <span class = "Apple-tab-span" style = "white-space: pre;"> </span>2030</strong></div> <div>   </div> <div > Boron in a free state is a colorless, gray or red crystalline or dark amorphous substance. Earlier than others, the well-known compound of Bora - Bura - is mentioned in the works of alchemists under the Arabic name "Burak" and Latin Borax, from which the name "boron" originated. Free Bor was first obtained by the French chemists J. Gay-Lussac and L. Thénard in 1808 by heating boric anhydride B2O3 with metallic potassium. & Nbsp; </div> <div> Boron has not been found in the free state in nature. Many boron compounds are widespread, especially in low concentrations. In the form of borosilicates, borates, boroaluminosilicates, and also as an isomorphic impurity in other minerals. Boron is part of many igneous and sedimentary rocks. Boron compounds are found in oil waters, seawater, salt lakes, hot springs, volcanic and hill mud, and in many soils. </div> <div>   </div>