When white phosphorous is stored for longer period it appears yellow due to :

Options

A. (A) The formation of oxide layer
B. (B) Conversion to another allotropic form
C. (C) The formation of mixture of its compounds
D. (D) None of the above

Answer

**Step-by-Step Solution:**

1. **Understanding White Phosphorus**: White phosphorus (P4) is a highly reactive allotrope of phosphorus. It is typically stored underwater or in inert gases to prevent it from reacting with oxygen in the air.

2. **Storage Conditions**: When white phosphorus is stored for a longer period, it can react with the oxygen present in the environment. This reaction leads to the formation of various phosphorus oxides.

3. **Formation of Phosphorus Pentoxide**: The primary product of this reaction is phosphorus pentoxide (P4O10). The formation of P4O10 occurs when white phosphorus reacts with oxygen, and this compound is known to have a yellowish color.

4. **Color Change**: As white phosphorus oxidizes and forms phosphorus pentoxide, the color of the stored phosphorus changes from white to yellow. This is due to the presence of the yellow phosphorus (another allotrope) that can form during the oxidation process.

5. **Conclusion**: Therefore, the appearance of yellow color in white phosphorus after prolonged storage is due to the formation of an oxide layer, specifically phosphorus pentoxide (P4O10).

**Final Answer**: When white phosphorus is stored for a longer period, it appears yellow due to the formation of an oxide layer (phosphorus pentoxide, P4O10).

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