In solid state PCl, is a ............

Options

A. covalent solid
B. octahedral structure
C. ionic solid with `[PCl_(6)]^(+)` octahedral and `[PCl_(4)]^(+)` tetrahedral
D. ionic solid with `[PCl_(4)]^(-)` tetrahedral and `[PCl_(6)]^(+)` octahedral

Explanation

To determine how PCl5 exists in the solid state, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Nature of PCl5**:
PCl5 (phosphorus pentachloride) is a compound that can exist in different forms depending on its state. In the solid state, it is important to analyze its ionic characteristics.

2. **Determine Ionic or Covalent Nature**:
PCl5 is known to exist as an ionic solid in the solid state. This means it has both cationic and anionic components.

3. **Identify the Cation and Anion**:
In the case of PCl5, it can be dissociated into PCl4^+ (cation) and PCl6^- (anion). Here, PCl4^+ is the positively charged ion, and PCl6^- is the negatively charged ion.

4. **Analyze the Geometry**:
- For the anion PCl6^-, we can calculate its steric number. The steric number is determined by the formula:
\[ \text{Steric Number} = \frac{\text{Valence Electrons}}{2} + \text{Monovalent Atoms} \]
For PCl6^-, the steric number is 6, which corresponds to an octahedral geometry.
- For the cation PCl4^+, we apply the same formula:
\[ \text{Steric Number} = \frac{\text{Valence Electrons}}{2} + \text{Monovalent Atoms} - 1 \]
For PCl4^+, the steric number is 4, which corresponds to a tetrahedral geometry.

5. **Conclusion**:
Therefore, in the solid state, PCl5 exists as an ionic solid composed of PCl4^+ ions and PCl6^- ions, where PCl6^- has an octahedral geometry and PCl4^+ has a tetrahedral geometry.

### Final Answer:
In solid state, PCl5 exists as an ionic solid with PCl4^+ (tetrahedral) and PCl6^- (octahedral).

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