There are several forms of solid phosphorus but only red and white forms are important. The white phosphorus consists of discrete tetrahedral `P_(4)` molecules. The structure of red phosphorus has not yet been completely determinated but there are evidences that it is polymeric and consists of chains of `P_(4)` tetrahdedral linked together. at room temperature , stable modification of elements phosphorus is red form. because of its highly polymerised structure, it is less volatile and less reactive than white phosphorus. in most of its compounds, phosphorus can have a valency of 3 or 5. phosphorus acid is peculiar because although it contains three hydrogen atoms per molecule, only two dissociation. When P is burnt in excess of `O_(2)`, a compound is obtained in which each molecules containsA. four atoms of P and six atoms of OB. four atoms of P and tenC. atoms of OD. two atoms of P and three atoms of O