Which is the correct increasing order of boiling points of the following compounds?

Options

A. Butane `lt` 1-Chlorobutane `lt` 1-Bromobutane `lt` 1-Iodobutane
B. 1-Iodobutane `lt `1-Bromobutane `lt` 1-Chlorobutane `lt` Butane
C. Butane `lt` 1-Iodobutane `lt` 1-Bromobutane `lt` 1-Chlorobutane
D. Butane `lt` 1-Chlorobutane `lt` 1-Iodobutane `lt` 1-Bromobutane

Explanation

To determine the correct increasing order of boiling points for the compounds Butane, Chlorobutane, Bromobutane, and Iodobutane, we need to consider the factors that influence boiling points, such as molecular weight and intermolecular forces.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds we are comparing are:
- Butane (C4H10)
- Chlorobutane (C4H9Cl)
- Bromobutane (C4H9Br)
- Iodobutane (C4H9I)

2. **Understand the Structure**: All these compounds have a similar carbon chain structure (4 carbon atoms), but differ in the halogen atom attached to one of the carbon atoms:
- Butane has only hydrogen atoms.
- Chlorobutane has a chlorine atom.
- Bromobutane has a bromine atom.
- Iodobutane has an iodine atom.

3. **Consider Molecular Weights**: The boiling point of a compound generally increases with increasing molecular weight due to stronger London dispersion forces:
- Molecular weight of Butane = 58 g/mol (C4H10)
- Molecular weight of Chlorobutane = 93.5 g/mol (C4H9Cl)
- Molecular weight of Bromobutane = 137 g/mol (C4H9Br)
- Molecular weight of Iodobutane = 184 g/mol (C4H9I)

4. **Rank the Compounds by Molecular Weight**: Based on the molecular weights:
- Butane (58 g/mol) has the lowest molecular weight.
- Chlorobutane (93.5 g/mol) is next.
- Bromobutane (137 g/mol) follows.
- Iodobutane (184 g/mol) has the highest molecular weight.

5. **Determine the Boiling Points**: Since boiling points increase with molecular weight:
- Butane will have the lowest boiling point.
- Chlorobutane will have a higher boiling point than Butane.
- Bromobutane will have a higher boiling point than Chlorobutane.
- Iodobutane will have the highest boiling point.

6. **Write the Increasing Order**: Therefore, the correct increasing order of boiling points is:
- Butane < Chlorobutane < Bromobutane < Iodobutane

### Final Answer:
The correct increasing order of boiling points is:
**Butane < Chlorobutane < Bromobutane < Iodobutane**