Some pairs of acids are given below. Select the pair in which second acid is stronger than first

Options

A. `CH_3CO_(2)H and CH_2FCO_2H`
B. `CH_2FCO_2H and CH_2ClCO_2H`
C. `CH_2ClCO_(2)H and CH_2BrCO_(2)H`
D. `CH_3CH_2CHFCO_2H and CH_3CHFCH_2CO_2H`

Explanation

To determine which pair of acids has the second acid stronger than the first, we need to analyze the acidic strength of each pair based on the substituents attached to the carboxylic acid group. The acidic strength of an acid is influenced by the electron-withdrawing or electron-donating effects of substituents.

### Step-by-Step Solution:

1. **Understand Acid Strength**: Acid strength is determined by the ability to donate a proton (H⁺). The more stable the conjugate base after losing H⁺, the stronger the acid. Electron-withdrawing groups (EWGs) stabilize the negative charge on the conjugate base, making the acid stronger.

2. **Analyze the Given Options**:
- **Option 1**: CH₃COOH (acetic acid) vs. CH₂FCOOH (fluoroacetic acid)
- CH₃COOH has no strong electron-withdrawing group.
- CH₂FCOOH has a fluorine atom, which is a strong EWG due to its -I effect. Therefore, CH₂FCOOH is stronger than CH₃COOH.

- **Option 2**: HF vs. HCl
- HF is a weaker acid than HCl because Cl is a better EWG than F due to its larger size and lower electronegativity. Thus, HCl is stronger than HF.

- **Option 3**: HCl vs. HBr
- HCl is stronger than HBr. Chlorine has a greater -I effect than bromine, making HCl the stronger acid.

- **Option 4**: CH₂FCOOH vs. CH₃CF₂COOH
- In this case, both acids have fluorine, but in CH₃CF₂COOH, the fluorine atoms are further away from the carboxylic group, which reduces the -I effect. Therefore, CH₂FCOOH is stronger than CH₃CF₂COOH.

3. **Conclusion**: The only pair where the second acid is stronger than the first is **Option 1: CH₃COOH vs. CH₂FCOOH**.

### Final Answer:
The correct answer is **Option 1: CH₃COOH (weaker) vs. CH₂FCOOH (stronger)**.