Which of the following are arranged in the decreasing order of dipole moment ?

Options

A. `CH_3Cl, CH_3Br, CH_3F`
B. `CH_3Cl, CH_3F, CH_3Br`
C. `CH_3Br, CH_3Cl, CH_3F`
D. `CH_3Br, CH_3F, CH_3Cl`

Explanation

To determine the decreasing order of dipole moments for the compounds CH3Cl, CH3Br, and CH3F, we need to consider the electronegativity of the halogens involved and the molecular structure of each compound.

### Step-by-Step Solution:

1. **Understand Dipole Moment**:
The dipole moment (μ) is a measure of the separation of positive and negative charges in a molecule and is calculated as:
\[ \mu = q \times d \]
where \(q\) is the charge and \(d\) is the distance between the charges.

2. **Identify the Electronegativity of Halogens**:
The electronegativity values of the halogens are as follows:
- Fluorine (F): 4.0
- Chlorine (Cl): 3.0
- Bromine (Br): 2.8

Since fluorine is the most electronegative, it will attract electrons more strongly than chlorine and bromine.

3. **Analyze Each Compound**:
- **CH3F**: The C-F bond will have a significant dipole moment due to the high electronegativity of fluorine, creating a strong partial negative charge on fluorine and a corresponding partial positive charge on carbon.
- **CH3Cl**: The C-Cl bond has a lower dipole moment than C-F due to chlorine's lower electronegativity compared to fluorine, but it is still significant.
- **CH3Br**: The C-Br bond has the least dipole moment among these three because bromine is the least electronegative of the three halogens, resulting in a smaller charge separation.

4. **Consider the Distance Factor**:
Although the dipole moment also depends on the distance between the charges, in this case, the electronegativity differences are more significant. The distance between the carbon and the halogen atoms is relatively similar across these compounds.

5. **Order the Dipole Moments**:
Based on the analysis:
- CH3F has the highest dipole moment due to the strong electronegativity of fluorine.
- CH3Cl has a moderate dipole moment.
- CH3Br has the lowest dipole moment.

Therefore, the decreasing order of dipole moments is:
\[ \text{CH3F} > \text{CH3Cl} > \text{CH3Br} \]

### Final Answer:
The correct order for decreasing dipole moment is:
\[ \text{CH3F} > \text{CH3Cl} > \text{CH3Br} \]