Phosphorus pentachloride in the solid exists as :

Options

A. `PCl_(5)`
B. `PCl_(4)^(+)Cl^(-)`
C. `PCl_(4)^(+)PCl_(6)^(-)`
D. `PCl_(5). Cl_(2)`

Answer

To determine how phosphorus pentachloride (PCl5) exists in the solid state, we need to analyze its structure and the nature of its bonding.

### Step-by-Step Solution:

1. **Understanding Phosphorus Pentachloride (PCl5):**
- Phosphorus pentachloride is a chemical compound composed of one phosphorus atom and five chlorine atoms. It is often encountered in both gaseous and solid states.

2. **Solid State Characteristics:**
- In the solid state, PCl5 forms a crystalline structure. It is important to note that the solid form of PCl5 is different from its gaseous form.

3. **Ionic vs. Covalent Nature:**
- While PCl5 is covalent in nature when in the gaseous state, in the solid state, it tends to exhibit ionic characteristics due to the presence of cations and anions.

4. **Formation of Ions:**
- In the solid state, PCl5 can dissociate into cations and anions. Specifically, it can exist as:
- Cation: \( PCl_4^+ \) (tetrahedral geometry)
- Anion: \( PCl_6^- \) (octahedral geometry)

5. **Conclusion:**
- Therefore, in the solid state, phosphorus pentachloride exists as \( PCl_4^+ \) and \( PCl_6^- \). This indicates that the correct answer to the question is option C: \( PCl_4^+ + PCl_6^- \).

### Final Answer:
**C: \( PCl_4^+ + PCl_6^- \)**

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