Which of the following molecules has trigonal planar geometry ?

Options

A. `BF_3`
B. `NH_3`
C. `H_2O`
D. `IF_3`

Answer

To determine which of the given molecules has a trigonal planar geometry, we will analyze each option step by step.

### Step 1: Analyze BF3
1. **Identify the central atom**: In BF3, the central atom is boron (B).
2. **Count valence electrons**: Boron has 3 valence electrons.
3. **Draw the structure**: Boron is bonded to three fluorine (F) atoms with single bonds.
4. **Calculate steric number**:
- Number of sigma bonds = 3 (one bond with each fluorine)
- Number of lone pairs = 0 (boron has no lone pairs)
- Steric number = 3 + 0 = 3
5. **Determine hybridization**:
- With a steric number of 3, the hybridization is sp².
6. **Determine geometry**:
- The geometry corresponding to sp² hybridization is trigonal planar.

### Step 2: Analyze NH3
1. **Identify the central atom**: In NH3, the central atom is nitrogen (N).
2. **Count valence electrons**: Nitrogen has 5 valence electrons.
3. **Draw the structure**: Nitrogen is bonded to three hydrogen (H) atoms with single bonds and has one lone pair.
4. **Calculate steric number**:
- Number of sigma bonds = 3 (one bond with each hydrogen)
- Number of lone pairs = 1
- Steric number = 3 + 1 = 4
5. **Determine hybridization**:
- With a steric number of 4, the hybridization is sp³.
6. **Determine geometry**:
- The geometry corresponding to sp³ hybridization is tetrahedral.

### Step 3: Analyze H2O
1. **Identify the central atom**: In H2O, the central atom is oxygen (O).
2. **Count valence electrons**: Oxygen has 6 valence electrons.
3. **Draw the structure**: Oxygen is bonded to two hydrogen atoms with single bonds and has two lone pairs.
4. **Calculate steric number**:
- Number of sigma bonds = 2 (one bond with each hydrogen)
- Number of lone pairs = 2
- Steric number = 2 + 2 = 4
5. **Determine hybridization**:
- With a steric number of 4, the hybridization is sp³.
6. **Determine geometry**:
- The geometry corresponding to sp³ hybridization is also tetrahedral.

### Step 4: Analyze IF3
1. **Identify the central atom**: In IF3, the central atom is iodine (I).
2. **Count valence electrons**: Iodine has 7 valence electrons.
3. **Draw the structure**: Iodine is bonded to three fluorine atoms with single bonds and has two lone pairs.
4. **Calculate steric number**:
- Number of sigma bonds = 3 (one bond with each fluorine)
- Number of lone pairs = 2
- Steric number = 3 + 2 = 5
5. **Determine hybridization**:
- With a steric number of 5, the hybridization is sp³d.
6. **Determine geometry**:
- The geometry corresponding to sp³d hybridization is trigonal bipyramidal.

### Conclusion
Based on the analysis:
- **BF3** has a trigonal planar geometry.
- **NH3** has a tetrahedral geometry.
- **H2O** has a tetrahedral geometry.
- **IF3** has a trigonal bipyramidal geometry.

Thus, the molecule with trigonal planar geometry is **BF3**.