`PCl_5` in solid state exists as.

Options

A. `PCl_5`
B. `PCl_4^(oplus)`
C. `PCl_6`
D. `PCl_4 ^(oplus) PCl_6^(Ө)`

Answer

To determine the form in which PCl₅ exists in the solid state, we need to analyze its structure and behavior in different states.

### Step-by-Step Solution:

1. **Understanding PCl₅ Structure in Gaseous State**:
- In the gaseous state, phosphorus pentachloride (PCl₅) exists as discrete PCl₅ molecules. Each molecule consists of one phosphorus atom bonded to five chlorine atoms. The molecular geometry is trigonal bipyramidal.

2. **Transition to Solid State**:
- When PCl₅ transitions from the gaseous state to the solid state, the interactions between the molecules change. In the solid state, the molecules are closely packed, and intermolecular forces become significant.

3. **Ionic Character in Solid State**:
- In the solid state, PCl₅ can exhibit ionic characteristics due to the polarization of the P-Cl bonds. This leads to the formation of charged species.

4. **Formation of Ions**:
- In the solid state, PCl₅ can dissociate into PCl₄⁺ and PCl₆⁻ ions. This means that one PCl₅ molecule can lose a chloride ion (Cl⁻) to form a PCl₄⁺ ion, while the lost chloride ion can associate with another PCl₅ molecule to form a PCl₆⁻ ion.

5. **Conclusion**:
- Therefore, in the solid state, PCl₅ exists as a combination of PCl₄⁺ and PCl₆⁻ ions. This ionic form stabilizes the structure of solid PCl₅.

### Final Answer:
PCl₅ in solid state exists as PCl₄⁺ and PCl₆⁻.