Red phosphorus may be prepared from white phosphorus by :

Options

A. adding red colour to white phosphorus
B. heating white phosphorus to red heat
C. heating white phosphorus at `250^(@)C` or at low temperature in the presence of sun light.
D. dissolving white phosphorus in `NaOH`

Answer

To prepare red phosphorus from white phosphorus, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structures**:
- White phosphorus (P4) has a tetrahedral structure with four phosphorus atoms forming a P4 molecule. It is known for its reactivity and is often found in a "bunch-like" structure.
- Red phosphorus, on the other hand, has a polymeric structure where phosphorus atoms are linked together in chains or networks. This structure is more stable and less reactive than white phosphorus.

2. **Conversion Process**:
- The conversion from white phosphorus to red phosphorus involves breaking the P-P bonds in the white phosphorus and forming new bonds to create the polymeric structure of red phosphorus.

3. **Heating the White Phosphorus**:
- To initiate the conversion, white phosphorus needs to be heated. The recommended temperature for this process is around 250 degrees Celsius. This temperature is sufficient to break the bonds in white phosphorus without completely destroying the phosphorus molecules.

4. **Presence of Sunlight**:
- The conversion can also occur in the presence of sunlight, which provides the necessary energy to facilitate the bond-breaking process. However, the primary method is through controlled heating.

5. **Final Result**:
- After heating white phosphorus at the specified temperature, it transforms into red phosphorus, which is characterized by its polymeric structure.

### Conclusion:
The correct method to prepare red phosphorus from white phosphorus is by heating white phosphorus at approximately 250 degrees Celsius or in the presence of sunlight.