Arrange the following in decreasing order of solubility in water
(i) `CH_(3)CH_(2)OH` (ii) `CH_(3)OH` (iii) `C_(6)H_(5)CH_(2)OH`.

Answer

To determine the decreasing order of solubility in water for the given alcohols, we will analyze the structure and stability of the carbocations formed from each alcohol. The three alcohols given are:

1. Ethanol (CH₃CH₂OH)
2. Methanol (CH₃OH)
3. Benzyl alcohol (C₆H₅CH₂OH)

### Step 1: Identify the type of alcohols
- **Ethanol (CH₃CH₂OH)**: This is a primary alcohol with two carbon atoms.
- **Methanol (CH₃OH)**: This is also a primary alcohol but with only one carbon atom.
- **Benzyl alcohol (C₆H₅CH₂OH)**: This is a primary alcohol, but it has a phenyl group (C₆H₅) attached to the carbon bearing the hydroxyl group.

### Step 2: Analyze the stability of the carbocations
When these alcohols are dissolved in water, they can form carbocations:
- **Ethanol** forms a primary carbocation (CH₃CH₂⁺), which is less stable.
- **Methanol** forms a primary carbocation (CH₃⁺), which is also less stable.
- **Benzyl alcohol** forms a benzyl carbocation (C₆H₅CH₂⁺), which is stabilized by resonance from the phenyl group.

### Step 3: Determine the order of stability of the carbocations
The stability of carbocations is ranked as follows:
- Tertiary > Secondary > Primary
- The benzyl carbocation is more stable than the primary carbocations due to resonance stabilization.

### Step 4: Relate stability to solubility
- The less stable the carbocation, the more soluble the alcohol is in water.
- Therefore, we can conclude that:
- Methanol (least stable carbocation) will be the most soluble.
- Ethanol (next least stable) will be the second most soluble.
- Benzyl alcohol (most stable carbocation) will be the least soluble.

### Final Order of Solubility
Thus, the order of solubility in water from most soluble to least soluble is:
1. **Methanol (CH₃OH)**
2. **Ethanol (CH₃CH₂OH)**
3. **Benzyl alcohol (C₆H₅CH₂OH)**