Which of the following is not a valid resonating structure?

Options

A.
B.
C.
D.

Explanation

To determine which of the following is not a valid resonating structure, we need to analyze the given structures based on the octet rule and the capacity of elements to accommodate electrons.

### Step-by-Step Solution:

1. **Identify the Elements Involved**:
- Look at the elements in the resonating structures. The key elements to focus on are Nitrogen (N) and Carbon (C), particularly since the question revolves around the second period elements.

**Hint**: Remember that elements in the second period (like Nitrogen and Carbon) have a limitation on the number of electrons they can accommodate due to the absence of d-orbitals.

2. **Check the Octet Rule**:
- For second-period elements, they cannot have more than 8 electrons in their valence shell. This is known as the octet rule.

**Hint**: Count the total number of electrons around the central atom in each structure to see if they exceed 8.

3. **Analyze Each Structure**:
- **Structure 1**: If it shows Nitrogen with 4 bonds, it has a total of 8 electrons (4 bonds = 8 electrons). This is valid.
- **Structure 2**: If it shows Carbon with 4 bonds, it also has 8 electrons. This is valid.
- **Structure 3**: If it shows Nitrogen with 3 bond pairs and a double bond, leading to 10 electrons in total, this structure is invalid as Nitrogen cannot accommodate more than 8 electrons.
- **Structure 4**: If it shows Carbon with 4 bonds and Nitrogen with 6 electrons (2 from a double bond and 4 from single bonds), this is valid.

**Hint**: Pay special attention to the number of bonds and the resulting electron count for each structure.

4. **Conclusion**:
- The structure that shows Nitrogen with 10 electrons is not a valid resonating structure because it violates the octet rule. Thus, the answer is the third option.

### Final Answer:
The resonating structure that is not valid is the third option where Nitrogen has more than 8 electrons.