Which of the following structural formulas is not properly
identified ?

Options

A. Ethane `H-undersetundersetH|oversetoversetH|C-undersetundersetH|oversetoversetH|C-H`
B. Methane `H-undersetundersetH|oversetoversetH|C-H`
C. Pentane `H-undersetundersetH|oversetoversetH|C-undersetundersetH|oversetoversetH|C-undersetundersetH|oversetoversetH|C-undersetundersetH|oversetoversetH|C-H`
D. Propane `H-undersetundersetH|oversetoversetH|C-undersetundersetH|oversetoversetH|C-undersetundersetH|oversetoversetH|C-H`.

Explanation

To determine which structural formula is not properly identified, we need to analyze each given structure based on the number of carbon atoms and their corresponding hydrogen atoms according to the general formula for alkanes, which is CnH2n+2.

### Step-by-Step Solution:

1. **Identify Ethane**:
- Ethane has 2 carbon atoms.
- Using the formula: CnH2n+2, for n=2:
- C2H(2*2 + 2) = C2H6
- The structure given for ethane corresponds to C2H6, which is correct.

2. **Identify Methane**:
- Methane has 1 carbon atom.
- Using the formula: CnH2n+2, for n=1:
- C1H(2*1 + 2) = C1H4
- The structure given for methane corresponds to C1H4, which is correct.

3. **Identify Butane**:
- Butane has 4 carbon atoms.
- Using the formula: CnH2n+2, for n=4:
- C4H(2*4 + 2) = C4H10
- The structure given shows 4 carbon atoms and corresponds to C4H10, which is correct.

4. **Identify Pentane**:
- Pentane has 5 carbon atoms.
- Using the formula: CnH2n+2, for n=5:
- C5H(2*5 + 2) = C5H12
- The structure given shows only 4 carbon atoms, which corresponds to butane (C4H10), not pentane. Therefore, this structure is not properly identified.

### Conclusion:
The structural formula that is not properly identified is the one representing pentane, which is actually showing the structure of butane.

### Answer:
Option 3 (Pentane) is not properly identified.

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