Phosphine produced smoky rings when it comes in contact with air because

Options

A. it reacts with water vapours
B. it reacts with nitrogen
C. it burns in air
D. it contains impurities of `P_(2)H_(4)`

Explanation

To solve the question of why phosphine (PH₃) produces smoky rings when it comes in contact with air, we can break down the reasoning step by step.

### Step-by-Step Solution:

1. **Understanding Phosphine**: Phosphine is a colorless, flammable gas with a distinct odor. It is represented by the chemical formula PH₃.

2. **Contact with Air**: When phosphine is exposed to air, it interacts with the components present in the atmosphere, primarily oxygen and nitrogen.

3. **Possible Reactions**:
- Phosphine can react with oxygen, leading to combustion. However, pure phosphine does not produce smoky rings upon combustion.
- The presence of water vapor in the air could potentially react with phosphine, but this is not the primary reason for the smoky rings.
- Nitrogen in the air does not react significantly with phosphine.

4. **Impurities in Phosphine**: The key to understanding the smoky rings lies in the impurities present in phosphine. Commercially available phosphine often contains impurities, particularly diphosphine (P₂H₄).

5. **Role of Diphosphine**: Diphosphine (P₂H₄) is known to be spontaneously flammable. When phosphine containing diphosphine comes into contact with air, the diphosphine reacts with oxygen, leading to incomplete combustion. This incomplete combustion produces carbon particles, which appear as smoky rings.

6. **Conclusion**: Therefore, the reason phosphine produces smoky rings when it comes in contact with air is due to the presence of impurities, specifically diphosphine (P₂H₄), which is spontaneously flammable and leads to the formation of smoke.

### Final Answer:
Phosphine produces smoky rings when it comes in contact with air because it contains impurities of P₂H₄ (diphosphine), which is spontaneously flammable.

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