Which one of the following arrangements of molecules is correct on the basic of their dipole moments?

Options

A. `NH_(3) gt BF_(3) gt NF_(3)`
B. `NH_(3) gt NF_(3) gt BF_(3)`
C. `BF_(3) gt NH_(3) gt NF_(3)`
D. `BF_(3) gt NF_(3) gt NH_(3)`

Explanation

To determine the correct arrangement of molecules based on their dipole moments, we need to analyze the molecular structures and their corresponding dipole moments for the given molecules: ammonia (NH3), nitrogen trifluoride (NF3), and boron trifluoride (BF3).

### Step-by-Step Solution:

1. **Analyze the structure of Ammonia (NH3)**:
- Ammonia has a trigonal pyramidal shape due to the presence of a lone pair on the nitrogen atom.
- The dipole moments from the N-H bonds point towards the nitrogen atom, and the lone pair contributes to the net dipole moment.
- The net dipole moment (μ1) is directed upwards (towards the lone pair) and is not equal to zero.

**Hint**: Remember that the presence of lone pairs affects the molecular geometry and the resultant dipole moment.

2. **Analyze the structure of Nitrogen Trifluoride (NF3)**:
- NF3 also has a trigonal pyramidal shape similar to NH3, but the dipole moments from the N-F bonds point towards the more electronegative fluorine atoms.
- The net dipole moment (μ2) is directed towards the fluorine atoms but is less than that of NH3 because the dipole moments from the N-F bonds partially cancel out due to the geometry.

**Hint**: Consider how the electronegativity of atoms affects the direction and magnitude of the dipole moments.

3. **Analyze the structure of Boron Trifluoride (BF3)**:
- BF3 has a trigonal planar structure, and the dipole moments from the B-F bonds are symmetrically arranged.
- Due to this symmetry, the individual dipole moments cancel each other out, resulting in a net dipole moment (μ3) of zero.

**Hint**: Symmetry in molecular geometry can lead to cancellation of dipole moments.

4. **Compare the dipole moments**:
- From the analysis:
- μ1 (NH3) > μ2 (NF3) > μ3 (BF3)
- Therefore, the order of dipole moments is:
- μ3 < μ2 < μ1

5. **Conclusion**:
- The correct arrangement of the dipole moments for the molecules is:
- BF3 < NF3 < NH3
- Thus, the answer to the question is option B.

### Summary of Dipole Moment Order:
- BF3 (μ3 = 0) < NF3 (μ2) < NH3 (μ1)