Carbon a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is
Thickness (graph theory) Thickness (graph theory) In graph theory, the thickness of a graph is the minimum number of planar graphs into which the edges of can be partitioned. That is, if there exists a collection of planar graphs, all having the same set of vertices, such that the union of these planar graphs is , then the thickness of is at most . In other words, the thickness of a graph is the minimum number of planar subgraphs whose union equals to graph . Thus, a planar graph has thickness 1. Graphs of thickness 2 are called biplanar graphs. The concept of