Phosphorus in glass jar. Phosphorus (P) is a poisonous, non-metallic element of the pnictogen group (Group 5). It is stored under water because it catches fire spontaneously in air. It is insoluble in water, but soluble in carbon disulphide. Phosphorus is an essential component of living systems, found in nervous tissue and bones, for example. It is also a key component of biological molecules such as DNA and RNA. Phosphorus is also used in the manufacture of matches and fireworks.