Which one of the following violates octet rule ?

Options

A. `NH_(3)`
B. `CH_(4)`
C. `CO_(2)`
D. NO

Explanation

To determine which of the following molecules violates the octet rule, we will analyze each molecule provided: ammonia (NH3), methane (CH4), carbon dioxide (CO2), and nitrogen monoxide (NO).

### Step-by-Step Solution:

1. **Understanding the Octet Rule**:
The octet rule states that atoms tend to form compounds in such a way that each atom has eight electrons in its valence shell, achieving a stable electron configuration similar to that of noble gases. If a central atom has more than eight electrons (electron efficient) or fewer than eight electrons (electron deficient), it violates the octet rule.

2. **Analyzing Ammonia (NH3)**:
- Central Atom: Nitrogen (N)
- Atomic Number of Nitrogen: 7 (Electronic configuration: 1s² 2s² 2p³)
- Nitrogen needs 3 more electrons to complete its octet.
- In NH3, nitrogen shares three electrons with three hydrogen atoms.
- Total electrons around nitrogen: 2 (from N-H bonds) + 2 (from lone pair) = 8 electrons.
- **Conclusion**: NH3 follows the octet rule.

3. **Analyzing Methane (CH4)**:
- Central Atom: Carbon (C)
- Atomic Number of Carbon: 6 (Electronic configuration: 1s² 2s² 2p²)
- Carbon needs 4 more electrons to complete its octet.
- In CH4, carbon shares four electrons with four hydrogen atoms.
- Total electrons around carbon: 2 (from each C-H bond) = 8 electrons.
- **Conclusion**: CH4 follows the octet rule.

4. **Analyzing Carbon Dioxide (CO2)**:
- Central Atom: Carbon (C)
- Carbon needs 4 electrons to complete its octet.
- In CO2, carbon forms double bonds with two oxygen atoms.
- Each oxygen needs 2 electrons, and carbon shares its 4 electrons (2 with each oxygen).
- Total electrons around carbon: 2 (from each double bond) = 8 electrons.
- **Conclusion**: CO2 follows the octet rule.

5. **Analyzing Nitrogen Monoxide (NO)**:
- Central Atom: Nitrogen (N)
- Nitrogen needs 3 more electrons to complete its octet.
- In NO, nitrogen forms a double bond with oxygen.
- Total electrons around nitrogen: 1 (from the bond with oxygen) + 6 (from lone pair) = 7 electrons.
- **Conclusion**: NO has only 7 electrons, making it electron deficient and violating the octet rule.

### Final Conclusion:
Among the given molecules, **Nitrogen Monoxide (NO)** is the only one that violates the octet rule.