To determine which compound has the least dipole moment among the given options, we will analyze the molecular structures and electronegativities of each compound.
### Step-by-Step Solution:
1. **Identify the Compounds**:
We need to analyze the dipole moments of the following compounds: PH3, CHCl3, NH3, and BF3.
2. **Analyze PH3 (Phosphine)**:
- Phosphorus (P) has 5 valence electrons, and each Hydrogen (H) has 1 valence electron.
- In PH3, there are 3 P-H bonds and 1 lone pair on phosphorus.
- The bond angle is approximately 93 degrees.
- The electronegativity of H is 2.2 and P is 2.19, making the P-H bond nearly non-polar.
- The dipole moment of PH3 is approximately 0.58 D.
3. **Analyze CHCl3 (Chloroform)**:
- Carbon (C) has 4 valence electrons, and Chlorine (Cl) has 7 valence electrons.
- In CHCl3, there are 3 C-Cl bonds and 1 C-H bond, with no lone pairs.
- The molecule has a tetrahedral shape.
- The electronegativities are C (2.5), H (2.2), and Cl (3.0).
- The dipole moments from C to Cl are significant, leading to a net dipole moment of approximately 1.15 D.
4. **Analyze NH3 (Ammonia)**:
- Nitrogen (N) has 5 valence electrons, and each H has 1 valence electron.
- In NH3, there are 3 N-H bonds and 1 lone pair on nitrogen.
- The shape is trigonal pyramidal due to the lone pair.
- The electronegativities are N (3.0) and H (2.2).
- The dipole moment of NH3 is approximately 1.46 D.
5. **Analyze BF3 (Boron Trifluoride)**:
- Boron (B) has 3 valence electrons, and each F has 7 valence electrons.
- In BF3, there are 3 B-F bonds and no lone pairs.
- The shape is trigonal planar.
- The electronegativity of B is 2.0 and F is 4.0.
- The dipole moments from B to F are significant, but since the molecule is symmetrical, the net dipole moment is 0 D.
6. **Compare the Dipole Moments**:
- PH3: 0.58 D
- CHCl3: 1.15 D
- NH3: 1.46 D
- BF3: 0 D
7. **Conclusion**:
The compound with the least dipole moment is **BF3**, as it has a net dipole moment of 0 D due to its symmetrical structure.
