Which of the following has the lowest boiling point ?

Options

A. (a)
B. (b)
C. (c)
D. (d)

Explanation

To determine which compound has the lowest boiling point among the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Relationship Between Boiling Point and Molecular Structure**:
- The boiling point of a compound is influenced by the strength of intermolecular forces, which include Van der Waals forces (dispersion forces).
- Generally, larger molecules with more surface area have stronger intermolecular forces, leading to higher boiling points.

2. **Identify the Types of Compounds**:
- The question involves different hydrocarbons, specifically alkanes, alkenes, and possibly alkynes.
- Alkanes are saturated hydrocarbons (single bonds), alkenes have at least one double bond, and alkynes have at least one triple bond.

3. **Compare the Boiling Points of Different Hydrocarbons**:
- Alkenes and alkynes typically have higher boiling points than alkanes due to the presence of stronger intermolecular forces (due to double and triple bonds).
- Therefore, among the given options, alkanes will generally have the lowest boiling point.

4. **Analyze the Specific Structures Provided**:
- If the options include straight-chain alkanes with different carbon counts, the boiling point increases with the number of carbon atoms.
- For example, a straight-chain alkane with 5 carbon atoms will have a higher boiling point than one with 4 carbon atoms.

5. **Determine the Lowest Boiling Point**:
- After analyzing the structures, if we find two alkanes, one with 4 carbons and another with 5 carbons, the one with 4 carbons will have the lowest boiling point.
- Thus, the correct answer is the compound with the least number of carbon atoms.

### Conclusion:
- The compound with the lowest boiling point among the options provided is the one that is a straight-chain alkane with 4 carbon atoms.