Which of the following is least reactive?

Options

A. White phosphorus
B. Yellow phosphorus
C. Red phosphorus
D. Black phosphorus

Explanation

To determine which form of phosphorus is the least reactive among white phosphorus, yellow phosphorus, red phosphorus, and black phosphorus, we can analyze the stability and reactivity of each form.

### Step-by-Step Solution:

1. **Identify the Forms of Phosphorus**:
- The four forms of phosphorus mentioned are:
- White Phosphorus
- Yellow Phosphorus
- Red Phosphorus
- Black Phosphorus

2. **Understand the Stability of Each Form**:
- **White Phosphorus**: Highly reactive and can ignite spontaneously in air.
- **Yellow Phosphorus**: Similar to white phosphorus but slightly more stable.
- **Red Phosphorus**: More stable than white and yellow phosphorus; it does not ignite easily and is less reactive.
- **Black Phosphorus**: The most stable form of phosphorus, highly polymerized, and has a layered structure.

3. **Analyze Reactivity Based on Stability**:
- Reactivity is inversely proportional to stability. This means that the more stable a substance is, the less reactive it will be.
- Since black phosphorus is the most stable form, it will be the least reactive.

4. **Conclusion**:
- Among the given options, black phosphorus is the least reactive form of phosphorus due to its high stability.

### Final Answer:
**D. Black Phosphorus is the least reactive form of phosphorus.**