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 given compounds is not tetrahedral in shape, we will analyze the hybridization and steric number of each compound. The compounds to consider are NH4+, SiCl4, SF4, and SO4^2-.

### Step-by-Step Solution:

1. **Identify the Central Atom and Valence Electrons:**
- For NH4+: The central atom is Nitrogen (N), which has 5 valence electrons.
- For SiCl4: The central atom is Silicon (Si), which has 4 valence electrons.
- For SF4: The central atom is Sulfur (S), which has 6 valence electrons.
- For SO4^2-: The central atom is Sulfur (S), which has 6 valence electrons.

2. **Calculate the Steric Number:**
- The steric number can be calculated using the formula:
\[ \text{Steric Number} = \frac{1}{2} \left( B + M + \text{Charge} \right) \]
where \( B \) is the number of bonding electrons, \( M \) is the number of monovalent atoms, and the charge is adjusted for cations or anions.

- **For NH4+:**
- Valence electrons (N) = 5
- Monovalent atoms (H) = 4
- Charge = -1 (since it's a cation, we subtract 1)
- Steric Number = \( \frac{1}{2} (5 + 4 - 1) = \frac{1}{2} (8) = 4 \)

- **For SiCl4:**
- Valence electrons (Si) = 4
- Monovalent atoms (Cl) = 4
- Charge = 0
- Steric Number = \( \frac{1}{2} (4 + 4 + 0) = \frac{1}{2} (8) = 4 \)

- **For SF4:**
- Valence electrons (S) = 6
- Monovalent atoms (F) = 4
- Charge = 0
- Steric Number = \( \frac{1}{2} (6 + 4 + 0) = \frac{1}{2} (10) = 5 \)

- **For SO4^2-:**
- Valence electrons (S) = 6
- Monovalent atoms (O) = 4
- Charge = -2
- Steric Number = \( \frac{1}{2} (6 + 4 + 2) = \frac{1}{2} (12) = 6 \)

3. **Determine Hybridization and Shape:**
- **NH4+:** Steric number = 4 → sp³ hybridized → Tetrahedral shape.
- **SiCl4:** Steric number = 4 → sp³ hybridized → Tetrahedral shape.
- **SF4:** Steric number = 5 → sp³d hybridized → Seesaw shape (not tetrahedral).
- **SO4^2-:** Steric number = 4 → sp³ hybridized → Tetrahedral shape.

4. **Conclusion:**
- The only compound that is not tetrahedral in shape is **SF4**, which has a seesaw shape due to the presence of one lone pair.

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