Which of the following is not tetrahedral in shape?

Options

A. `NH_4^+`
B. `SiCl_4`
C. `SF_4`
D. `SO_4^(2-)`

Explanation

To determine which of the following compounds is not tetrahedral in shape, we need to analyze the molecular geometry of each compound based on the number of valence electrons and the presence of lone pairs.

### Step-by-step Solution:

1. **Identify the Compounds**: Let's assume we have the following compounds to analyze: NH₄⁺, SiCl₄, and SF₄.

2. **Count Valence Electrons**:
- **NH₄⁺**: Nitrogen (N) has 5 valence electrons, and each Hydrogen (H) has 1. The total is 5 + (4 × 1) = 9. Since it has a +1 charge, we subtract 1, giving us 8 valence electrons.
- **SiCl₄**: Silicon (Si) has 4 valence electrons, and each Chlorine (Cl) has 7. The total is 4 + (4 × 7) = 32 valence electrons.
- **SF₄**: Sulfur (S) has 6 valence electrons, and each Fluorine (F) has 7. The total is 6 + (4 × 7) = 34 valence electrons.

3. **Determine Hybridization**:
- For **NH₄⁺**: With 8 valence electrons, the hybridization is sp³, leading to a tetrahedral geometry.
- For **SiCl₄**: With 32 valence electrons, it also has a tetrahedral geometry (sp³ hybridization).
- For **SF₄**: With 34 valence electrons, it has 10 electrons, which corresponds to sp³d hybridization, leading to a trigonal bipyramidal geometry.

4. **Identify Shapes**:
- **NH₄⁺**: Tetrahedral shape (no lone pairs).
- **SiCl₄**: Tetrahedral shape (no lone pairs).
- **SF₄**: Trigonal bipyramidal geometry due to the presence of one lone pair.

5. **Conclusion**: Among the given compounds, **SF₄** is not tetrahedral in shape; it has a trigonal bipyramidal geometry.

### Final Answer:
The compound that is not tetrahedral in shape is **SF₄**.