Four aromatic carboxylic acids on heating with soda-lime at 630 K, give toluene as the only product. Write the structures of the four aromatic carboxylic acid.

Explanation

To solve the problem of identifying four aromatic carboxylic acids that yield toluene upon heating with soda-lime at 630 K, we will follow these steps:

### Step 1: Understand the Reaction
Soda-lime (a mixture of sodium hydroxide and calcium oxide) is used for the decarboxylation of carboxylic acids. During this process, the carboxyl group (-COOH) is removed as carbon dioxide (CO2), and the remaining hydrocarbon chain forms a hydrocarbon. In this case, we are looking for aromatic carboxylic acids that will yield toluene (C7H8) after decarboxylation.

### Step 2: Identify the Structure of Toluene
Toluene is a methyl-substituted benzene, which can be represented as:
```
...