The reason for (A) P2 which is similar to N2 molecule is not stable because (what is (A): (a) The bond energy of three (PP) bonds is more than (P-P) triple bond as opposed to N=N bond energy which is more than there (N-N) bond energy (A-gaseous) (b) Lattice energy of P-P is more than N-N bond energy (A = Solid state) (c) Lone pairs of electrons in P= Pis kinetically more reactive than those present on N2 in N=N(A solid state) (d) Kinetically P-P bond is more reactive than N-N bond (A = liquid) 2.
See as Like N2 phosphorous don't form P2...rather it form P4...in P4 each phosphorus is attached to three P atom by single bond...the Three P-P single bond has more energy than P P...