The correct structural formula of butanoic acid is

Options

A. `H-underset(H)underset(|)overset(H)overset(|)C-overset(H)overset(|)C=overset(H)overset(|)C-overset(O)overset(||)C-OH`
B. `H-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(O)overset(||)C-OH`
C. `H-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-OH`
D. `H-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-underset(H)underset(|)overset(H)overset(|)C-overset(O)overset(||)C-OH`

Explanation

To determine the correct structural formula of butanoic acid, we can follow these steps:

### Step 1: Identify the number of carbon atoms
Butanoic acid has the prefix "but," which indicates that it contains four carbon atoms.

### Step 2: Recognize the functional group
The term "acid" in butanoic acid signifies the presence of a carboxyl group (–COOH). This group is responsible for the acidic properties of the molecule.

### Step 3: Construct the carbon chain
Since butanoic acid has four carbon atoms, we will arrange them in a straight chain:
- C1 - C2 - C3 - C4

### Step 4: Attach the carboxyl group
The carboxyl group (–COOH) will be attached to the last carbon (C4) in the chain. Therefore, the structure now looks like this:
- C1 - C2 - C3 - C4(–COOH)

### Step 5: Complete the hydrogen atoms
Each carbon atom can form four bonds. We need to add hydrogen atoms to satisfy the valency of each carbon:
- C1 will have 3 H atoms (C1 - H3)
- C2 will have 2 H atoms (C2 - H2)
- C3 will have 2 H atoms (C3 - H2)
- C4 will have 1 H atom (C4 - H) because it is bonded to the carboxyl group.

### Step 6: Write the complete structural formula
Now, putting it all together, the complete structural formula of butanoic acid is:
```
H H O
| | ||
H--C--C--C--C--OH
| | |
H H H
```
This can also be represented as:
```
CH3-CH2-CH2-COOH
```

### Step 7: Identify the molecular formula
The molecular formula can be derived from the structural formula. For butanoic acid, it is C4H8O2.

### Final Answer
The correct structural formula of butanoic acid is:
```
CH3-CH2-CH2-COOH
```