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 of the following alcohols is the least soluble in water, we will analyze the solubility of each alcohol based on their molecular structure and the effect of the hydrocarbon chain length on solubility.

### Step-by-Step Solution:

1. **Identify the Alcohols**: The given alcohols are:
- Ethanol (C2H5OH)
- 1-Propanol (C3H7OH)
- 1-Butanol (C4H9OH)
- 1-Pentanol (C5H11OH)

2. **Understand the Solubility Concept**: Alcohols are generally soluble in water due to the ability to form hydrogen bonds with water molecules. The hydroxyl group (-OH) in alcohols is polar and can interact with the polar water molecules.

3. **Analyze the Hydrocarbon Chain**: The solubility of alcohols in water decreases as the length of the hydrocarbon chain increases. This is because:
- The longer the hydrocarbon chain, the more non-polar character the molecule has.
- Non-polar molecules do not interact favorably with polar solvents like water.

4. **Count the Carbon Atoms**:
- Ethanol has 2 carbon atoms.
- 1-Propanol has 3 carbon atoms.
- 1-Butanol has 4 carbon atoms.
- 1-Pentanol has 5 carbon atoms.

5. **Determine the Least Soluble Alcohol**: Based on the principle that longer hydrocarbon chains lead to decreased solubility:
- Ethanol (2 carbons) is more soluble than 1-Propanol (3 carbons).
- 1-Propanol (3 carbons) is more soluble than 1-Butanol (4 carbons).
- 1-Butanol (4 carbons) is more soluble than 1-Pentanol (5 carbons).

6. **Conclusion**: Since 1-Pentanol has the longest hydrocarbon chain (5 carbon atoms), it will be the least soluble in water.

### Final Answer:
The least soluble alcohol in water among the given options is **1-Pentanol**.

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