Choose the correct pair regarding dipole moment

Options

A. `CH_(3)Cl gt CH_(3)F`
B. `NH_(3) gt NF_(3)`
C. `HF gt HCl`
D. All of these

Answer

To solve the question regarding dipole moments, we will analyze each pair given in the options and determine their correctness based on the principles of dipole moments.

### Step-by-Step Solution:

1. **Understanding Dipole Moment**:
- The dipole moment (μ) is a vector quantity that indicates the polarity of a bond. It is defined as:
\[ \mu = Q \times D \]
where \( Q \) is the charge difference and \( D \) is the distance (bond length) between the charges.

2. **Analyzing the First Pair: CS3Cl and CS3F**:
- In CS3Cl, chlorine (Cl) is less electronegative than fluorine (F) in CS3F.
- The bond length between carbon and chlorine (C-Cl) is greater than that between carbon and fluorine (C-F) due to the larger size of chlorine.
- Therefore, the dipole moment of CS3F is less than that of CS3Cl:
\[ \mu_{CS3F} < \mu_{CS3Cl} \]
- **Conclusion**: This option is correct.

3. **Analyzing the Second Pair: NH3 and NF3**:
- Both NH3 and NF3 have a pyramidal structure.
- In NH3, the dipole moments from the N-H bonds add up in the same direction towards nitrogen (N).
- In NF3, the dipole moments from the N-F bonds point towards fluorine (F), while the dipole moment from the lone pair on nitrogen points in the opposite direction.
- Thus, the dipole moments in NH3 will add up, while in NF3 they will partially cancel out:
\[ \mu_{NH3} > \mu_{NF3} \]
- **Conclusion**: This option is correct.

4. **Analyzing the Third Pair: HCl and HF**:
- The electronegativity of fluorine (F) is greater than that of chlorine (Cl).
- Therefore, the dipole moment of HF, which has a greater electronegativity difference, will be greater than that of HCl:
\[ \mu_{HF} > \mu_{HCl} \]
- **Conclusion**: This option is correct.

5. **Final Conclusion**:
- Since all three pairs are correct, the answer is:
- **All of these are correct**.