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 chemical species and their geometries, we will analyze each species one by one, determining their hybridization, bond pairs, lone pairs, and geometrical shapes.

### Step-by-Step Solution:

1. **Analyze PCl5:**
- **Valence Electrons:** Phosphorus (P) is in group 15, so it has 5 valence electrons.
- **Monovalent Atoms:** There are 5 chlorine (Cl) atoms, contributing 5 monovalent electrons.
- **Hybridization Calculation:**
\[ \text{Hybridization} = \frac{\text{Valence Electrons} + \text{Monovalent Atoms}}{2} = \frac{5 + 5}{2} = 5 \]
Thus, the hybridization is \( sp^3d \).
- **Bond Pairs and Lone Pairs:** There are 5 bond pairs (one for each Cl) and 0 lone pairs.
- **Geometry:** The geometry of PCl5 is trigonal bipyramidal.
- **Given Geometry:** The question states it is trigonal planar, which is incorrect.

2. **Analyze SF6:**
- **Valence Electrons:** Sulfur (S) is in group 16, so it has 6 valence electrons.
- **Monovalent Atoms:** There are 6 fluorine (F) atoms, contributing 6 monovalent electrons.
- **Hybridization Calculation:**
\[ \text{Hybridization} = \frac{6 + 6}{2} = 6 \]
Thus, the hybridization is \( sp^3d^2 \).
- **Bond Pairs and Lone Pairs:** There are 6 bond pairs and 0 lone pairs.
- **Geometry:** The geometry of SF6 is octahedral.
- **Given Geometry:** The question states it is octahedral, which is correct.

3. **Analyze BeCl2:**
- **Valence Electrons:** Beryllium (Be) is in group 2, so it has 2 valence electrons.
- **Monovalent Atoms:** There are 2 chlorine (Cl) atoms, contributing 2 monovalent electrons.
- **Hybridization Calculation:**
\[ \text{Hybridization} = \frac{2 + 2}{2} = 2 \]
Thus, the hybridization is \( sp \).
- **Bond Pairs and Lone Pairs:** There are 2 bond pairs and 0 lone pairs.
- **Geometry:** The geometry of BeCl2 is linear.
- **Given Geometry:** The question states it is linear, which is correct.

4. **Analyze NH3:**
- **Valence Electrons:** Nitrogen (N) is in group 15, so it has 5 valence electrons.
- **Monovalent Atoms:** There are 3 hydrogen (H) atoms, contributing 3 monovalent electrons.
- **Hybridization Calculation:**
\[ \text{Hybridization} = \frac{5 + 3}{2} = 4 \]
Thus, the hybridization is \( sp^3 \).
- **Bond Pairs and Lone Pairs:** There are 3 bond pairs and 1 lone pair.
- **Geometry:** The geometry of NH3 is tetrahedral, but the shape is trigonal pyramidal due to the lone pair.
- **Given Geometry:** The question states it is trigonal pyramidal, which is correct.

### Conclusion:
The wrongly matched pair is **PCl5**, which is stated to have a trigonal planar geometry, but its actual geometry is trigonal bipyramidal.