Which of the following alcohols is the least soluble in water ?

Options

A. Ethanol
B. 1-Propanol
C. 1-Butanol
D. 1-Pentanol

Explanation

To determine which alcohol is the least soluble in water, we need to analyze the structure of the alcohols given and their respective carbon chain lengths. The solubility of alcohols in water primarily depends on the balance between the hydrophilic (water-attracting) hydroxyl (-OH) group and the hydrophobic (water-repelling) hydrocarbon chain.

### Step-by-Step Solution:

1. **Identify the Alcohols**:
We have four alcohols to consider:
- A: Propanol (C3H8O)
- B: Butanol (C4H10O)
- C: Pentanol (C5H12O)
- D: Hexanol (C6H14O)

2. **Understand Solubility Factors**:
Alcohols are soluble in water due to hydrogen bonding between the hydroxyl (-OH) group and water molecules. However, as the length of the hydrocarbon chain increases, the hydrophobic character of the alcohol increases, which reduces its solubility in water.

3. **Compare Carbon Chain Lengths**:
- Propanol has 3 carbon atoms.
- Butanol has 4 carbon atoms.
- Pentanol has 5 carbon atoms.
- Hexanol has 6 carbon atoms.

4. **Analyze the Impact of Carbon Chain Length**:
As the number of carbon atoms increases, the non-polar hydrocarbon part becomes larger compared to the polar -OH group. This leads to a decrease in solubility because the larger non-polar part does not interact favorably with water.

5. **Determine the Least Soluble Alcohol**:
Among the given options, Hexanol (D) has the longest carbon chain (6 carbon atoms), making it the least soluble in water due to its significant hydrophobic character.

### Conclusion:
The alcohol that is least soluble in water is **Hexanol (D)**.

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