Strongest and weakest acid among the following is
`CH_(3)-NO_(2) CH_(3)-CHO CH_(3)-F CH_(3)-CN`

Options

A. I and II
B. III and IV
C. III and II
D. I and III

Answer

To determine the strongest and weakest acids among the compounds CH₃NO₂ (Nitromethane), CH₃CHO (Acetaldehyde), CH₃F (Fluoromethane), and CH₃CN (Acetonitrile), we need to analyze the electron-withdrawing effects of the substituents attached to the carbon atom in each compound.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- CH₃NO₂ (Nitromethane)
- CH₃CHO (Acetaldehyde)
- CH₃F (Fluoromethane)
- CH₃CN (Acetonitrile)

2. **Understand Acid Strength:**
- Acids donate protons (H⁺ ions). The strength of an acid is influenced by the stability of the conjugate base formed after the acid donates a proton.
- Electron-withdrawing groups stabilize the negative charge on the conjugate base, making the acid stronger.

3. **Evaluate Electron-Withdrawing Groups:**
- **NO₂ (Nitro group)**: Strong electron-withdrawing group due to resonance and inductive effects.
- **CN (Cyanide group)**: Also a strong electron-withdrawing group, but slightly less effective than NO₂.
- **CHO (Aldehyde group)**: Moderate electron-withdrawing group.
- **F (Fluorine)**: Weak electron-withdrawing group compared to the others.

4. **Rank the Groups by Electron-Withdrawing Ability:**
- NO₂ > CN > CHO > F

5. **Determine the Strongest Acid:**
- CH₃NO₂ will be the strongest acid because the nitro group can stabilize the negative charge on the conjugate base effectively.

6. **Determine the Weakest Acid:**
- CH₃F will be the weakest acid because the fluorine group is the least effective at stabilizing the conjugate base.

7. **Conclusion:**
- **Strongest Acid**: CH₃NO₂ (Nitromethane)
- **Weakest Acid**: CH₃F (Fluoromethane)

### Final Answer:
- Strongest Acid: **CH₃NO₂**
- Weakest Acid: **CH₃F**