Rank the following compounds in increasing order of their acidity:
1. 3 - fluorobutanoic acid
2. 3 - chlorobutanoic acid
3. 2 - flurobutanoic acid
4. Butanoic acid
5. 4 - chlorobutanoic acid.

Options

A. `3 lt 1 lt 2 lt 4 lt 5`
B. `4 lt 3 lt 1 lt 2 lt 5`
C. `5 lt 2 lt 1 lt 3 lt 4`
D. `4 lt 5 lt 2 lt 1 lt 3`

Answer

To rank the given compounds in increasing order of their acidity, we need to analyze the effects of the substituents (fluorine and chlorine) and their positions relative to the carboxylic acid group (-COOH) in each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- 3-Fluorobutanoic acid
- 3-Chlorobutanoic acid
- 2-Fluorobutanoic acid
- Butanoic acid
- 4-Chlorobutanoic acid

2. **Understand Acidity**:
Acidity in carboxylic acids is influenced by the electronegativity of substituents and their distance from the carboxylic acid group. More electronegative groups (like fluorine) increase acidity more than less electronegative groups (like chlorine). Additionally, substituents closer to the -COOH group have a stronger effect on acidity.

3. **Rank the Compounds**:
- **Butanoic Acid**: This is the baseline compound without any electronegative substituents, so it will be the least acidic.
- **4-Chlorobutanoic Acid**: The chlorine is farthest from the -COOH group, so its effect on acidity is minimal. It will be the next least acidic.
- **3-Chlorobutanoic Acid**: Chlorine is closer to the -COOH group than in 4-chlorobutanoic acid, making it more acidic than 4-chlorobutanoic acid.
- **3-Fluorobutanoic Acid**: Fluorine is more electronegative than chlorine, and since it is in the same position as the 3-chloro compound, it will be more acidic than 3-chlorobutanoic acid.
- **2-Fluorobutanoic Acid**: The fluorine is closer to the -COOH group than in 3-fluorobutanoic acid, making it the most acidic of all.

4. **Final Ranking**:
- 1. Butanoic acid (least acidic)
- 2. 4-Chlorobutanoic acid
- 3. 3-Chlorobutanoic acid
- 4. 3-Fluorobutanoic acid
- 5. 2-Fluorobutanoic acid (most acidic)

### Increasing Order of Acidity:
1. Butanoic acid
2. 4-Chlorobutanoic acid
3. 3-Chlorobutanoic acid
4. 3-Fluorobutanoic acid
5. 2-Fluorobutanoic acid