Which of the following bond angle is not observed in `PCl_(5)` molecule in gaseous state?

Options

A. `120^(@)`
B. `180^(@)`
C. `90^(@)`
D. `60^(@)`

Explanation

To determine which bond angle is not observed in the PCl5 molecule in the gaseous state, we can follow these steps:

### Step 1: Understand the Structure of PCl5
PCl5 (phosphorus pentachloride) has a trigonal bipyramidal structure. This means that there are five chlorine atoms bonded to a central phosphorus atom.

### Step 2: Identify the Bond Angles
In a trigonal bipyramidal structure, there are specific bond angles:
- The axial positions (180 degrees apart)
- The equatorial positions (120 degrees apart)
- The angles between axial and equatorial positions (90 degrees)

### Step 3: Analyze the Bond Angles
1. **Axial-Axial Bond Angle**: 180 degrees
2. **Equatorial-Equatorial Bond Angle**: 120 degrees
3. **Axial-Equatorial Bond Angle**: 90 degrees

### Step 4: Identify the Missing Bond Angle
Now, we need to check the bond angles provided in the options to see which one is not present in PCl5. The angles we have identified are:
- 90 degrees
- 120 degrees
- 180 degrees

The angle that is not present in the PCl5 molecule is **60 degrees**.

### Conclusion
Thus, the bond angle that is not observed in the PCl5 molecule in the gaseous state is **60 degrees**.

### Final Answer
The answer is option **D: 60 degrees**.

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