Write the structural formulae and give IUPAC names of the following :
(i) Lactic acid , (ii) Tartaric acid
(iii) Isobutyric acid , (iv) Crotonic acid
(v) Salicylic acid , (vi) Terephthalic acid.

Explanation

To solve the question, we will write the structural formulae and provide the IUPAC names for the given carboxylic acids: Lactic acid, Tartaric acid, Isobutyric acid, Crotonic acid, Salicylic acid, and Terephthalic acid.

### Step-by-Step Solution:

1. **Lactic Acid**
- **IUPAC Name**: 2-hydroxypropanoic acid
- **Structural Formula**:
```
OH
|
CH3-CH-COOH
|
H
```
- Explanation: Lactic acid has three carbon atoms, with a hydroxyl group (-OH) on the second carbon and a carboxylic acid group (-COOH) on the first carbon.

2. **Tartaric Acid**
- **IUPAC Name**: 2,3-dihydroxybutanedioic acid
- **Structural Formula**:
```
HOOC-CHOH-CHOH-COOH
```
- Explanation: Tartaric acid has four carbon atoms, with two carboxylic acid groups at the terminal positions and hydroxyl groups on the second and third carbons.

3. **Isobutyric Acid**
- **IUPAC Name**: 2-methylpropanoic acid
- **Structural Formula**:
```
CH3
|
CH3-CH-COOH
```
- Explanation: Isobutyric acid has four carbon atoms, with a carboxylic acid group on the first carbon and a methyl group on the second carbon.

4. **Crotonic Acid**
- **IUPAC Name**: But-2-enoic acid
- **Structural Formula**:
```
CH2=CH-COOH
```
- Explanation: Crotonic acid has four carbon atoms, with a carboxylic acid group on the first carbon and a double bond between the second and third carbons.

5. **Salicylic Acid**
- **IUPAC Name**: 2-hydroxybenzoic acid
- **Structural Formula**:
```
OH
|
C6H4-COOH
```
- Explanation: Salicylic acid has a benzene ring with a carboxylic acid group and a hydroxyl group on the second carbon of the ring.

6. **Terephthalic Acid**
- **IUPAC Name**: 1,4-benzenedicarboxylic acid
- **Structural Formula**:
```
HOOC-C6H4-COOH
```
- Explanation: Terephthalic acid has a benzene ring with two carboxylic acid groups at the 1 and 4 positions.

### Summary of IUPAC Names and Structural Formulae:
1. Lactic Acid: 2-hydroxypropanoic acid
2. Tartaric Acid: 2,3-dihydroxybutanedioic acid
3. Isobutyric Acid: 2-methylpropanoic acid
4. Crotonic Acid: But-2-enoic acid
5. Salicylic Acid: 2-hydroxybenzoic acid
6. Terephthalic Acid: 1,4-benzenedicarboxylic acid