How many molecules among the following have zero dipole moment `NH_(3),BF_(3),NF_(3),C CI_(4)` ? .

Explanation

To determine how many molecules among NH₃, BF₃, NF₃, and CCl₄ have a zero dipole moment, we need to analyze the molecular geometry and symmetry of each molecule.

### Step-by-Step Solution:

1. **Analyze NH₃ (Ammonia)**:
- NH₃ has a trigonal pyramidal shape due to the presence of a lone pair on the nitrogen atom.
- The bond dipoles (N-H) do not cancel out because of the asymmetrical shape.
- **Conclusion**: NH₃ has a net dipole moment that is not zero.

2. **Analyze BF₃ (Boron Trifluoride)**:
- BF₃ has a trigonal planar geometry.
- The three bond dipoles (B-F) are symmetrically arranged around the boron atom.
- The bond dipoles cancel each other out due to symmetry.
- **Conclusion**: BF₃ has a net dipole moment of zero.

3. **Analyze NF₃ (Nitrogen Trifluoride)**:
- NF₃ has a trigonal pyramidal shape similar to NH₃ due to the presence of a lone pair on nitrogen.
- The bond dipoles (N-F) do not cancel out because of the asymmetrical shape.
- **Conclusion**: NF₃ has a net dipole moment that is not zero.

4. **Analyze CCl₄ (Carbon Tetrachloride)**:
- CCl₄ has a tetrahedral geometry.
- The four bond dipoles (C-Cl) are symmetrically arranged around the carbon atom.
- The bond dipoles cancel each other out due to symmetry.
- **Conclusion**: CCl₄ has a net dipole moment of zero.

### Final Answer:
Among the given molecules, **2 molecules (BF₃ and CCl₄)** have a zero dipole moment.

---