Final answer:
Phosphorus exists in three allotropes: white phosphorus as a toxic, waxy solid that can transition into liquid and gaseous states; red phosphorus as an amorphous substance; and black phosphorus as a crystalline solid.
Step-by-step explanation:
Phosphorus exists in three primary allotropes which are different forms with distinct arrangements of atoms and physical properties. These allotropes are white phosphorus, red phosphorus, and black phosphorus.
White phosphorus is a toxic, waxy solid that can exist as a solid, liquid, or gas because it has a melting point of 44.2 °C and boils at 280 °C.
Red phosphorus is an amorphous substance, while black phosphorus is an unreactive crystalline solid resembling graphite.
Phosphorus can thus be found naturally in the solid state but can be turned into liquid and gas through industrial processes or laboratory conditions. All phosphorus allotropes obey the octet rule, forming three bonds per phosphorus atom.