Which of the following acids is isomeriic with phthalic acid

Options

A. Succinic acid
B. Salicylic acid
C. 1,4-benzene dicarboxylic acid
D. Methyl benzoic acid

Explanation

To determine which acid is isomeric with phthalic acid, we need to understand the structure of phthalic acid and its possible isomers.

### Step-by-Step Solution:

1. **Identify the Structure of Phthalic Acid**:
- Phthalic acid is a benzene derivative with two carboxylic acid (-COOH) groups. The two -COOH groups are located at the 1 and 2 positions on the benzene ring (ortho position).
- The chemical formula for phthalic acid is C8H6O4.

2. **Determine Possible Isomers**:
- Isomers are compounds that have the same molecular formula but different structural arrangements. For dicarboxylic acids derived from benzene, we can have:
- Ortho (1,2-)
- Meta (1,3-)
- Para (1,4-)

3. **Identify the Isomers of Phthalic Acid**:
- **Ortho-phthalic acid**: This is phthalic acid itself.
- **Meta-phthalic acid**: This would have the -COOH groups at the 1 and 3 positions, known as isophthalic acid.
- **Para-phthalic acid**: This would have the -COOH groups at the 1 and 4 positions, known as terephthalic acid.

4. **Evaluate the Given Options**:
- The question asks which of the following acids is isomeric with phthalic acid. Based on the structural analysis:
- Isophthalic acid (1,3-benzenedicarboxylic acid) is isomeric with phthalic acid.
- Terephthalic acid (1,4-benzenedicarboxylic acid) is also isomeric with phthalic acid.
- Salicylic acid is not isomeric as it has a different structure.
- Methylbenzoic acid is also not isomeric with phthalic acid.

5. **Conclusion**:
- The acids that are isomeric with phthalic acid are isophthalic acid and terephthalic acid. However, if we need to select one based on the options given, the answer is **terephthalic acid (1,4-benzenedicarboxylic acid)**.

### Final Answer:
The acid that is isomeric with phthalic acid is **terephthalic acid (1,4-benzenedicarboxylic acid)**.