The alcohol having least solubility in water is

Options

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

Answer

To determine which alcohol has the least solubility in water, we need to consider the structure of alcohols and how their solubility is affected by the size of their alkyl groups.

### Step-by-Step Solution:

1. **Understand Alcohol Structure**: Alcohols consist of a hydroxyl (-OH) group attached to a carbon chain (alkyl group). The general formula for alcohols can be represented as R-OH, where R is the alkyl group.

2. **Identify the Influence of Alkyl Groups**: The solubility of alcohols in water is influenced by the size of the alkyl group. Alcohols with smaller alkyl groups tend to be more soluble in water because the polar -OH group can interact favorably with water molecules.

3. **Consider Examples of Alcohols**:
- Methanol (CH3OH) has a very small alkyl group (one carbon) and is highly soluble in water.
- Ethanol (C2H5OH) has a slightly larger alkyl group (two carbons) and is also soluble in water, but less so than methanol.
- Propanol (C3H7OH) has an even larger alkyl group (three carbons), resulting in lower solubility compared to methanol and ethanol.

4. **Evaluate Larger Alcohols**: As we continue to increase the size of the alkyl group, we reach alcohols like butanol (C4H9OH) and pentanol (C5H11OH). These larger alcohols have significantly reduced solubility in water due to the increased non-polar character of the larger alkyl group.

5. **Conclusion**: Among common alcohols, as the size of the alkyl group increases, the solubility in water decreases. Therefore, the alcohol with the largest alkyl group will have the least solubility in water.

For example, pentanol (C5H11OH) would be less soluble than butanol (C4H9OH), which in turn is less soluble than propanol (C3H7OH).

Thus, the alcohol having the least solubility in water is likely to be **pentanol (C5H11OH)** or another alcohol with a larger alkyl group.