Identify the wrongly matched pair.

Options

A. `PCl_5`- trigonal planar
B. `SF_6` -Octahedral
C. `BeCl_2`-Linear
D. `NH_3`-Trigonal pyramidal

Answer

To identify the wrongly matched pair among the given options, we will analyze the molecular geometry of each compound mentioned in the question.

### Step-by-Step Solution:

1. **Understanding the Structures**:
- We have four compounds to analyze: PCl5, SF6, BeCl2, and NH3.

2. **Analyzing NH3 (Ammonia)**:
- NH3 has one nitrogen atom with three hydrogen atoms bonded to it and one lone pair of electrons.
- The geometry of NH3 is pyramidal due to the presence of the lone pair.
- **Conclusion**: NH3 is correctly matched as triangular pyramidal.

3. **Analyzing BeCl2 (Beryllium Chloride)**:
- BeCl2 has one beryllium atom bonded to two chlorine atoms.
- Beryllium has no lone pairs and forms two single bonds with chlorine, resulting in a linear geometry.
- **Conclusion**: BeCl2 is correctly matched as linear.

4. **Analyzing SF6 (Sulfur Hexafluoride)**:
- SF6 has one sulfur atom bonded to six fluorine atoms.
- Sulfur has no lone pairs and forms six bonds, resulting in an octahedral geometry.
- **Conclusion**: SF6 is correctly matched as octahedral.

5. **Analyzing PCl5 (Phosphorus Pentachloride)**:
- PCl5 has one phosphorus atom bonded to five chlorine atoms.
- Phosphorus has no lone pairs and forms five bonds, resulting in a trigonal bipyramidal geometry.
- **Conclusion**: PCl5 is incorrectly matched as triangular planar; it should be trigonal bipyramidal.

### Final Answer:
The wrongly matched pair is **PCl5**, which is incorrectly described as having a triangular planar geometry instead of the correct trigonal bipyramidal geometry.