White phosphorous shows chemilumeniscence because it:

glows in the dark

The correct answer i option 3. glows in the dark.

Let  us explore why white phosphorus exhibits chemiluminescence and the relevant properties involved.

White Phosphorus and Chemiluminescence

Nature of White Phosphorus:

Appearance: White phosphorus is a waxy, translucent solid. It is often stored underwater or in inert gases to prevent its reaction with air.

Reactivity: White phosphorus is highly reactive with oxygen. It can spontaneously ignite in air at temperatures above about 30°C (86°F), forming phosphorus pentoxide (\(P_4O_{10}\)).

Chemiluminescence:

Chemiluminescence is the production of light as a result of a chemical reaction. This light emission occurs without the involvement of heat, which is a characteristic of phosphorescence and fluorescence.

Mechanism in White Phosphorus:

Oxidation Reaction: White phosphorus slowly reacts with oxygen in the air, forming phosphorus oxides. This reaction is exothermic (releases heat), but the amount of heat produced is not enough to raise the temperature significantly.

Reaction:

\(P_4 + 5O_2 \rightarrow P_4O_{10}\)

Light Emission: During this slow oxidation, phosphorus atoms can be excited to higher energy states. As these excited atoms return to their ground state, they release energy in the form of visible light. This is the chemiluminescence observed.

Detailed Explanation:

Thermodynamics of Reaction: The oxidation of phosphorus is a relatively slow process at room temperature, and it produces a faint glow because the reaction produces energy that is released as visible light.

Mechanism of Light Production: The oxidation of phosphorus can produce intermediate phosphorus oxides in low concentrations, and these intermediates can get excited. When these excited states return to their lower energy states, they emit photons (light).

While white phosphorus is highly toxic and poses severe health risks, this property does not contribute to its chemiluminescence. Toxicity is related to its reactivity and not to its ability to emit light.

Waxy: Its waxy nature refers to its physical appearance and is unrelated to its chemiluminescent properties.

Reacts in Inert Atmosphere: White phosphorus requires oxygen to react and produce light. An inert atmosphere (like nitrogen or argon) would prevent the oxidation reaction and therefore no chemiluminescence would be observed.

Summary: White phosphorus shows chemiluminescence because it glows in the dark due to its slow oxidation in the air, which produces a faint light. The underlying reaction and the subsequent emission of light are key aspects of this phenomenon.