The most unlikely representation of resonance structures of p-nitrophenoxide ion is :

Options

A.
B.
C.
D.

Answer

To determine the most unlikely representation of resonance structures of the p-nitrophenoxide ion, we need to analyze the possible resonance structures and identify which one does not conform to the rules of resonance.

### Step-by-Step Solution:

1. **Identify the Structure of p-Nitrophenoxide Ion**:
- The p-nitrophenoxide ion consists of a phenolic ring with a nitro group (-NO2) at the para position and a negatively charged oxygen (phenoxide ion).
- The basic structure can be represented as follows:
```
O^-
|
C6H4 - NO2
```

2. **Understand Resonance Structures**:
- Resonance structures are different ways of drawing the same molecule where only the positions of electrons differ, not the positions of the atoms.
- In p-nitrophenoxide, the negative charge on the oxygen can be delocalized through resonance.

3. **Draw Possible Resonance Structures**:
- **Structure 1**: The negative charge on the oxygen remains, and the double bond between the oxygen and carbon shifts to the ortho position.
- **Structure 2**: The negative charge moves to the ortho position, creating a double bond between the oxygen and the carbon.
- **Structure 3**: The nitro group can also participate in resonance, where the nitrogen can have a positive charge and the double bonds can shift accordingly.

4. **Evaluate Each Structure**:
- **Structure A**: This structure has a positive charge on the nitrogen and maintains the correct number of bonds. This is a valid resonance structure.
- **Structure B**: This structure shows multiple double bonds involving nitrogen, which is not possible since nitrogen can only form a maximum of four bonds. This structure is unlikely.
- **Structure C**: This structure has the negative charge on the ortho position, which is possible due to resonance.
- **Structure D**: This structure shows a single bond with a negative charge on oxygen, which is also valid.

5. **Identify the Most Unlikely Representation**:
- After evaluating the resonance structures, **Structure B** is the most unlikely representation because it violates the octet rule for nitrogen by having five bonds.

### Conclusion:
The most unlikely representation of resonance structures of p-nitrophenoxide ion is **Structure B**.