Which allotropic form of phosphorus shows chemiluminescence ?

Question

Accepted Answer

White phosphorus is the allotropic form of phosphorus that exhibits chemiluminescence. This phenomenon occurs when white phosphorus is exposed to oxygen, leading to a slow oxidation process that emits a faint glow in the dark. This glow is due to the release of energy in the form of light as the phosphorus oxidizes.

1. **Explanation for Option 1 (White Phosphorus):**
   - White phosphorus is highly reactive and unstable in the presence of oxygen. It spontaneously ignites at around 30°C in air, and during this oxidation process, it emits a faint greenish light, which is the chemiluminescence observed. This property is unique to white phosphorus among the allotropes of phosphorus, making it the correct answer.

2. **Explanation for why other options are incorrect:**
   - **Option 2 (Red Phosphorus):** Red phosphorus is more stable and less reactive than white phosphorus. It does not exhibit chemiluminescence because it does not oxidize in the same manner as white phosphorus. Red phosphorus requires higher temperatures to react with oxygen and does not emit light during this process.
   - **Option 3 (a-Black Phosphorus):** a-Black phosphorus is a more stable and less reactive form of phosphorus. It does not show chemiluminescence because it does not undergo the same rapid oxidation process as white phosphorus. Its structure and properties do not support the emission of light.
   - **Option 4 (B-Black Phosphorus):** Similar to a-black phosphorus, B-black phosphorus is stable and does not react with oxygen in a way that would produce chemiluminescence. It lacks the necessary reactivity and structural characteristics to emit light during oxidation.

In conclusion, white phosphorus is the only allotropic form of phosphorus that exhibits chemiluminescence due to its high reactivity and the nature of its oxidation process. This makes Option 1 the correct answer.