Allotropy of phosphorus: White phosphorus shows maximum stability under which of the following general conditions?

Introduction / Context:
Phosphorus exists in several allotropes (white, red, black) with differing stability and reactivity. White phosphorus (P4) is the most reactive form and must be handled carefully. The question asks under what common laboratory conditions white phosphorus is comparatively most stable to storage and handling.

Given Data / Assumptions:

• Focus is on practical stability against oxidation and conversion to other allotropes.
• Options include pressure, temperature, and environmental exposure.
• Assume simple laboratory storage practices.

Concept / Approach:
White phosphorus is pyrophoric in air near ambient temperatures and is light-sensitive; it oxidizes and can ignite spontaneously. It is typically stored under water, in the dark, at room temperature and atmospheric pressure to exclude oxygen and light, which suppress reactivity and slow conversion to red phosphorus. High temperatures or illumination accelerate transformation to red or black phosphorus and enhance oxidation hazards; very high pressure/high temperature favor other allotropes rather than P4 stability.

Step-by-Step Solution:

Verification / Alternative check:
Safety data sheets and inorganic chemistry texts recommend storage of white phosphorus under water in light-proof containers, confirming best-practice stability conditions.

Why Other Options Are Wrong:

• Very high pressure: not a practical stabilization method; can promote other phases.
• Room temperature in dry air with light: unsafe; risk of ignition and rapid oxidation.
• > 600°C in air or vacuum at high temperature: conditions would convert/oxidize P4.

Common Pitfalls:
Assuming “room temperature” alone is sufficient; exposure to air and light makes white phosphorus hazardous even at room temperature unless submerged.

Final Answer:
Atmospheric pressure in the dark under water.