Allotropes Of Phosphorus

The difference in reactivity between phosphorus allotropes stems from their structures. White phosphorus consists of discrete tetrahedral P_4 molecules in which the P-P-P bond angles are only about 60 degrees, far less than the ideal angle, creating considerable angular strain. This strain makes the bonds weak and reactive, so white phosphorus ignites readily in air and is highly toxic. Red phosphorus has a polymeric chain structure in which the P_4 units are linked together, relieving much of the strain and giving a more stable, less reactive, and non-toxic solid. The option that white phosphorus has a stable layered structure is wrong, since that describes neither allotrope correctly. The option that red phosphorus is monatomic is false. The option that white phosphorus is a gas is incorrect, as it is a waxy solid. This structural basis for differing reactivity is a standard NCERT comparison. Such questions reward conceptual clarity, since a student who truly grasps white phosphorus can solve many superficially different variants with the same approach. A common JEE pitfall is to ignore the role of white phosphorus, yet it is exactly this factor that distinguishes the correct answer from the tempting alternatives. Plausibility check: the strained sixty-degree angles in P_4 explain white phosphorus's spontaneous ignition, confirming the structural reasoning.