Which is the correct arrangement of the molecules based on dipole moments ?

Options

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

Explanation

To determine the correct arrangement of the molecules based on their dipole moments, let's analyze each molecule step by step.

### Step 1: Analyze BF3 (Boron Trifluoride)
1. **Structure**: BF3 has a trigonal planar structure because boron has three valence electrons and forms three bonds with fluorine atoms.
2. **Dipole Moment**: Each B-F bond is polar due to the electronegativity difference between boron and fluorine. However, because of the symmetrical arrangement of the three bonds, the dipole moments cancel each other out.
3. **Conclusion**: The dipole moment of BF3 is zero.

### Step 2: Analyze NF3 (Nitrogen Trifluoride)
1. **Structure**: NF3 has a trigonal pyramidal shape due to the presence of one lone pair on the nitrogen atom and three bond pairs with fluorine atoms.
2. **Dipole Moment**: The dipole moments of the N-F bonds do not cancel out completely because of the lone pair. The dipole moments point towards the fluorine atoms, resulting in a net dipole moment directed upwards.
3. **Conclusion**: NF3 has a non-zero dipole moment.

### Step 3: Analyze NH3 (Ammonia)
1. **Structure**: NH3 also has a trigonal pyramidal shape, similar to NF3, because it has one lone pair on nitrogen and three bond pairs with hydrogen atoms.
2. **Dipole Moment**: The dipole moments of the N-H bonds point towards the nitrogen atom, and since all dipoles are directed upwards, they add up constructively.
3. **Conclusion**: NH3 has a higher dipole moment than NF3 due to the arrangement of dipole moments.

### Step 4: Compare Dipole Moments
Now, we can compare the dipole moments of the three molecules:
- **BF3**: Dipole moment = 0 (least)
- **NF3**: Dipole moment > 0 (greater than BF3)
- **NH3**: Dipole moment > NF3 (highest)

### Final Arrangement
Based on the analysis, the correct arrangement of the molecules based on their dipole moments is:
1. NH3 (highest dipole moment)
2. NF3
3. BF3 (least dipole moment)

### Summary
The correct order of dipole moments from highest to lowest is:
**NH3 > NF3 > BF3**

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