Which one of the following has the lowest boiling point ?

Options

A. `CH_2Cl`
B. `C_2H_5Cl`
C. `C_2H_5Br`
D. `C_2H_5I`

Explanation

To determine which of the given alkyl halides has the lowest boiling point, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- C2H5-Cl (Ethyl Chloride)
- C2H5-Br (Ethyl Bromide)
- C2H5-I (Ethyl Iodide)

2. **Understand the Factors Affecting Boiling Point**: The boiling point of alkyl halides is influenced by:
- Molecular mass: Higher molecular mass generally leads to a higher boiling point.
- Branching: More branching in the molecule typically leads to a lower boiling point.

3. **Compare the Molecular Masses**:
- **C2H5-Cl**:
- Molecular mass = (2 × 12) + (5 × 1) + (1 × 35.5) = 24 + 5 + 35.5 = 64.5 g/mol
- **C2H5-Br**:
- Molecular mass = (2 × 12) + (5 × 1) + (1 × 79.9) = 24 + 5 + 79.9 = 108.9 g/mol
- **C2H5-I**:
- Molecular mass = (2 × 12) + (5 × 1) + (1 × 126.9) = 24 + 5 + 126.9 = 155.9 g/mol

4. **Analyze the Results**:
- C2H5-Cl has a molecular mass of 64.5 g/mol.
- C2H5-Br has a molecular mass of 108.9 g/mol.
- C2H5-I has a molecular mass of 155.9 g/mol.
- From this, we can see that C2H5-Cl has the lowest molecular mass.

5. **Conclusion**: Since boiling point is directly proportional to molecular mass, C2H5-Cl (Ethyl Chloride) will have the lowest boiling point among the three compounds.

### Final Answer:
**C2H5-Cl (Ethyl Chloride) has the lowest boiling point.**

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