Among the following methyl halides the one with the highest value of dipole moment is :

Options

A. `CH_3F`
B. `CH_3CI`
C. `CH_3Br`
D. `CH_3I`

Answer

To determine which methyl halide has the highest dipole moment among CH3F, CH3Cl, CH3Br, and CH3I, we can follow these steps:

### Step 1: Understand Dipole Moment
The dipole moment is a measure of the separation of positive and negative charges in a molecule. It depends on the electronegativity of the atoms involved and the molecular geometry.

### Step 2: Identify Electronegativity of Halogens
The halogens (Group 17) have the following electronegativities:
- Fluorine (F) - highest electronegativity
- Chlorine (Cl)
- Bromine (Br)
- Iodine (I) - lowest electronegativity

### Step 3: Analyze Each Methyl Halide
1. **CH3F**: Contains fluorine, which has the highest electronegativity, leading to a significant dipole moment.
2. **CH3Cl**: Contains chlorine, which has a lower electronegativity than fluorine but higher than bromine and iodine.
3. **CH3Br**: Contains bromine, which has lower electronegativity than chlorine.
4. **CH3I**: Contains iodine, which has the lowest electronegativity among the halogens listed.

### Step 4: Consider Molecular Size and Electronegativity
While electronegativity is crucial, the size of the atom also plays a role. Chlorine, being larger than fluorine, can exhibit an abnormal behavior in terms of dipole moment due to its size and the bond length.

### Step 5: Determine the Order of Dipole Moments
Based on the above analysis, we can establish the order of dipole moments:
- CH3Cl (highest dipole moment)
- CH3F
- CH3Br
- CH3I (lowest dipole moment)

### Conclusion
Thus, the methyl halide with the highest value of dipole moment is **CH3Cl**.

### Final Answer
**CH3Cl** (Option B)