Correct Lewis structure is:

Options

A. `[:underset(..)overset(..)O-C=underset(..)overset(..)N:]^(-)`
B. `[C=C:]^(2-)`
C. `[:underset(..)overset(..)Cl-underset(..)overset(..)O:]^(-)`
D. `:overset(..)N=overset(..)O:`

Explanation

To determine the correct Lewis structure from the given options, we will analyze each structure step by step, focusing on the octet rule and the distribution of electrons.

### Step-by-Step Solution:

1. **Analyze the First Structure:**
- The first structure shows oxygen with three lone pairs, a single bond to carbon, and carbon double bonded to nitrogen, which has three lone pairs and a negative charge.
- Count the electrons around oxygen: 6 (from lone pairs) + 2 (from the bond with carbon) = 8 electrons. **Oxygen's octet is complete.**
- Count the electrons around carbon: 2 (from the bond with oxygen) + 4 (from the double bond with nitrogen) = 6 electrons. **Carbon's octet is incomplete.**
- **Conclusion:** This structure is incorrect because carbon does not have a complete octet.

2. **Analyze the Second Structure:**
- The second structure shows carbon double bonded to another carbon, with a lone pair and a 2- charge.
- Count the electrons around the first carbon: 4 (from the double bond) = 4 electrons. **This carbon's octet is incomplete.**
- Count the electrons around the second carbon: 4 (from the double bond) + 2 (from the lone pair) = 6 electrons. **This carbon's octet is also incomplete.**
- **Conclusion:** This structure is incorrect because both carbons do not have complete octets.

3. **Analyze the Third Structure:**
- The third structure shows chlorine with 6 electrons (3 lone pairs) and oxygen with 6 electrons (3 lone pairs) and a negative charge.
- Count the electrons around chlorine: 6 (from lone pairs) + 2 (from the bond with oxygen) = 8 electrons. **Chlorine's octet is complete.**
- Count the electrons around oxygen: 6 (from lone pairs) + 2 (from the bond with chlorine) = 8 electrons. **Oxygen's octet is complete.**
- **Conclusion:** This structure is correct because both chlorine and oxygen have complete octets.

4. **Analyze the Fourth Structure:**
- The fourth structure shows nitrogen with a complete octet and oxygen also with a complete octet.
- Count the electrons around nitrogen: 2 (from bonds) + 6 (from lone pairs) = 8 electrons. **Nitrogen's octet is complete.**
- Count the electrons around oxygen: 6 (from lone pairs) + 2 (from the bond with nitrogen) = 8 electrons. **Oxygen's octet is complete.**
- However, nitrogen in its non-bonded state has 5 electrons (3 from lone pairs and 2 from bonds), which is not possible.
- **Conclusion:** This structure is incorrect because nitrogen cannot have an incomplete octet in its non-bonded state.

### Final Conclusion:
The only correct Lewis structure is the third one, where both chlorine and oxygen have complete octets.

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