The correct order of acidic strength of the following is
(I) Oxalic acid `HOOC-COOH`
(II) Malonic acid
`HOOC-CH_(2)-COOH`
(III) Succinic acid
`HOOC-(CH_(2))_(2)-COOH`
(IV) Glutaric acid
`HOOC-(CH_(2))_(3)-COOH`

Options

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

Answer

To determine the correct order of acidic strength among the given dicarboxylic acids, we need to analyze the stability of their conjugate bases after they lose a proton (H⁺). The conjugate base of a dicarboxylic acid is a carboxylate ion, which is stabilized by electron-withdrawing groups and destabilized by electron-donating groups (like alkyl groups).

### Step-by-Step Solution:

1. **Identify the Compounds:**
- (I) Oxalic acid: `HOOC-COOH`
- (II) Malonic acid: `HOOC-CH₂-COOH`
- (III) Succinic acid: `HOOC-(CH₂)₂-COOH`
- (IV) Glutaric acid: `HOOC-(CH₂)₃-COOH`

2. **Understand the Effect of Alkyl Groups:**
- Alkyl groups exert a +I (inductive) effect, which increases electron density on the carboxylate ion formed after deprotonation. This destabilizes the conjugate base, leading to a decrease in acidic strength.

3. **Analyze Each Acid:**
- **Oxalic Acid (I):** Has no alkyl groups, so it has the highest acidic strength because its conjugate base is the most stabilized.
- **Malonic Acid (II):** Contains one alkyl group (CH₂), which exerts a +I effect, thus reducing acidic strength compared to oxalic acid.
- **Succinic Acid (III):** Contains two alkyl groups (CH₂-CH₂), further increasing the +I effect and reducing acidic strength compared to malonic acid.
- **Glutaric Acid (IV):** Contains three alkyl groups (CH₂-CH₂-CH₂), which will exert the most +I effect, making it the least acidic.

4. **Order of Acidic Strength:**
- Based on the analysis, the order of acidic strength from strongest to weakest is:
- (I) Oxalic acid > (II) Malonic acid > (III) Succinic acid > (IV) Glutaric acid.

5. **Final Answer:**
- The correct order of acidic strength is:
- **Oxalic acid > Malonic acid > Succinic acid > Glutaric acid.**