Arrange increasing order of acidic strength of following dibasic acids:
(I) oxalic acid. `" "`(II) succinic acid `" "` (III) malonic acid `" "`(IV) adipic acid

Options

A. `III lt II lt I lt IV`
B. `II lt III gt I gt IV`
C. `I gt III gt II gt IV`
D. `II gt I gt III lt IV`

Answer

To determine the increasing order of acidic strength of the given dibasic acids (oxalic acid, succinic acid, malonic acid, and adipic acid), we need to analyze the structures and the effects of substituents on the acidity.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **Oxalic Acid (I)**: HOOC-COOH
- **Malonic Acid (III)**: HOOC-CH2-COOH
- **Succinic Acid (II)**: HOOC-CH2-CH2-COOH
- **Adipic Acid (IV)**: HOOC-CH2-CH2-CH2-COOH

2. **Understand the Acidic Strength**:
- The acidic strength of dibasic acids is influenced by the presence of electron-withdrawing groups (EWGs) and electron-donating groups (EDGs).
- EWGs increase acidity by stabilizing the negative charge on the conjugate base (after deprotonation).
- EDGs decrease acidity by destabilizing the conjugate base.

3. **Analyze Each Acid**:
- **Oxalic Acid**: Contains two carboxylic acid groups directly bonded to each other. The strong EWG effect of both carboxyl groups enhances acidity.
- **Malonic Acid**: Has one carbon chain (CH2) between the two carboxyl groups. This reduces the EWG effect slightly compared to oxalic acid, but it is still relatively acidic.
- **Succinic Acid**: Contains two CH2 groups between the carboxyl groups. This further reduces the EWG effect, making it less acidic than malonic acid.
- **Adipic Acid**: Has four carbon atoms between the two carboxyl groups, which significantly reduces the EWG effect, making it the least acidic among the four.

4. **Rank the Acids**:
- Based on the analysis, we can rank the acids from least acidic to most acidic:
- Adipic Acid (IV) < Succinic Acid (II) < Malonic Acid (III) < Oxalic Acid (I)

5. **Final Order**:
- The increasing order of acidic strength is:
- **Adipic Acid (IV) < Succinic Acid (II) < Malonic Acid (III) < Oxalic Acid (I)**

### Increasing Order of Acidic Strength:
**Adipic Acid (IV) < Succinic Acid (II) < Malonic Acid (III) < Oxalic Acid (I)**