White and red phosphorus exhibit different physical and chemical properties. Which statement is true for both white phosphorus and red phosphorus?

Introduction / Context:Allotropes of phosphorus differ in reactivity and solubility. White phosphorus is highly reactive, pyrophoric when finely divided, and soluble in CS2; red phosphorus is more polymeric, less reactive, and insoluble in CS2. Questions often test recognition of properties that apply to one or both allotropes.

Given Data / Assumptions:

• Allotropes considered: white and red phosphorus only.
• We seek a property valid for both forms.
• Conditions: typical laboratory/industrial handling under air and heating.

Concept / Approach:Combustion behavior: both allotropes will burn in air when sufficiently heated, forming phosphorus oxides. Solubility: only white P is soluble in carbon disulfide; red P is insoluble. Reaction with hot concentrated alkali to produce phosphine is characteristic of white P; red P is far less reactive, and the same reaction does not proceed comparably under standard conditions.

Step-by-Step Solution:Evaluate CS2 solubility: true for white P; false for red P.Evaluate combustion: both can combust when heated in air, though white P ignites more readily.Evaluate reaction with hot alkali: characteristic for white P; not reliably for red P under standard conditions.Therefore, the common true statement is that both burn when heated in air.

Verification / Alternative check:References list red P as less reactive yet combustible at elevated temperatures; white P is readily combustible and must be stored under water to prevent oxidation/ignition.

Why Other Options Are Wrong:Solubility in CS2 applies only to white P.Reaction with hot caustic to give phosphine is primarily a property of white P; red P does not behave the same way in typical conditions.“All of the above” fails because (a) and (c) are not universally true.

Common Pitfalls:Assuming similar behavior due to same element; overlooking allotrope-specific properties, especially solubility and reactivity differences.

Final Answer:Both burn when heated in air.