Which of the following species has tetrahedral geometry?

Options

A. `BF_(4)^(-)`
B. `CH_(4)`
C. `NH_(4)^(+)`
D. all these

Explanation

To determine which of the given species has tetrahedral geometry, we need to calculate the steric number for each species. The steric number can be calculated using the formula:

**Steric Number = (Number of Valence Electrons of Central Atom) + (Number of Monovalent Atoms) - (Charge)**

Let's analyze the species mentioned in the transcript: BF4^-, CH4, and NH4^+.

### Step 1: Calculate the Steric Number for BF4^-
1. **Identify the central atom**: Boron (B).
2. **Determine the valence electrons for Boron**: Boron has 3 valence electrons.
3. **Count the number of monovalent atoms (F)**: There are 4 fluorine atoms, each contributing 1 valence electron.
4. **Account for the charge**: Since it is a negative ion (BF4^-), we add 1 to the total.
5. **Calculate**:
- Valence electrons of B = 3
- Valence electrons from F = 4 (1 for each of the 4 F atoms)
- Charge = -1 (add 1)
- Total = 3 + 4 + 1 = 8
- Steric Number = 8 / 2 = 4

### Step 2: Calculate the Steric Number for CH4
1. **Identify the central atom**: Carbon (C).
2. **Determine the valence electrons for Carbon**: Carbon has 4 valence electrons.
3. **Count the number of monovalent atoms (H)**: There are 4 hydrogen atoms.
4. **Calculate**:
- Valence electrons of C = 4
- Valence electrons from H = 4 (1 for each of the 4 H atoms)
- Total = 4 + 4 = 8
- Steric Number = 8 / 2 = 4

### Step 3: Calculate the Steric Number for NH4^+
1. **Identify the central atom**: Nitrogen (N).
2. **Determine the valence electrons for Nitrogen**: Nitrogen has 5 valence electrons.
3. **Count the number of monovalent atoms (H)**: There are 4 hydrogen atoms.
4. **Account for the charge**: Since it is a positive ion (NH4^+), we subtract 1 from the total.
5. **Calculate**:
- Valence electrons of N = 5
- Valence electrons from H = 4 (1 for each of the 4 H atoms)
- Charge = +1 (subtract 1)
- Total = 5 + 4 - 1 = 8
- Steric Number = 8 / 2 = 4

### Conclusion
All three species (BF4^-, CH4, and NH4^+) have a steric number of 4, which corresponds to tetrahedral geometry.

### Final Answer
The species that has tetrahedral geometry are BF4^-, CH4, and NH4^+.