Which of the following allotropes of phosphorus is most reactive?

allotropy, the existence of a chemical element in two or more forms, which may differ in the arrangement of atoms in crystalline solids or in the occurrence of molecules that contain different numbers of atoms

White phosphorus occurs as discrete P4 units , where P atom lie at the corners of a regular tetrahedron 

White phosphorus is discrete ${\mathrm{P}}_4$ molecule.