Which of the following is most acidic ?

Options

A. `H_2O`
B. `CH_3OH`
C. `C_2H_5OH`
D. `CH_3CH_2CH_2OH`

Answer

To determine which of the given compounds is the most acidic, we need to analyze the acidity of each compound based on their ability to donate a proton (H⁺) and the stability of the resulting conjugate base (the anion formed after the proton is lost).

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- Water (H₂O)
- Methanol (CH₃OH)
- Ethanol (C₂H₅OH)
- Propanol (CH₃CH₂OH)

2. **Understanding Acidity**: Acidity is determined by the ability of a compound to donate a proton (H⁺). When a compound donates a proton, it forms a conjugate base. The stability of this conjugate base is crucial in determining the acidity of the original compound.

3. **Formation of Conjugate Bases**:
- For water (H₂O), the conjugate base is OH⁻.
- For methanol (CH₃OH), the conjugate base is CH₃O⁻.
- For ethanol (C₂H₅OH), the conjugate base is C₂H₅O⁻.
- For propanol (CH₃CH₂OH), the conjugate base is CH₃CH₂O⁻.

4. **Stability of Conjugate Bases**: The stability of the conjugate base is influenced by the inductive effect of the alkyl groups attached to the oxygen atom. Alkyl groups are electron-donating, which can destabilize the negative charge on the conjugate base.
- OH⁻ (from water) is less destabilized by any alkyl groups.
- CH₃O⁻ (from methanol) is destabilized by the methyl group.
- C₂H₅O⁻ (from ethanol) is destabilized by the ethyl group.
- CH₃CH₂O⁻ (from propanol) is destabilized by the propyl group.

5. **Comparing Acidity**: Since the conjugate base of water (OH⁻) is the least destabilized by alkyl groups, it is more stable compared to the conjugate bases of methanol, ethanol, and propanol. Therefore, water is the most acidic among the given compounds.

### Conclusion:
The most acidic compound among the given options is **Water (H₂O)**.

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