The octet rule is not obeyed in :

Options

A. `CO_(2)`
B. `Zn^(2+)`
C. `SiCl_(4)`
D. CO

Explanation

To determine which compound does not obey the octet rule, we will analyze each option provided in the question step by step.

### Step 1: Analyze Option A - CO2 (Carbon Dioxide)
- The structure of CO2 consists of one carbon atom double-bonded to two oxygen atoms.
- The Lewis structure can be represented as: O=C=O.
- Carbon shares four electrons (two double bonds) with oxygen, and each oxygen atom has two lone pairs, making a total of eight electrons around each oxygen.
- Therefore, carbon has four electrons from the double bonds and completes its octet with the shared electrons.
- **Conclusion**: CO2 obeys the octet rule.

### Step 2: Analyze Option B - Zn²⁺ (Zinc Ion)
- The electronic configuration of Zn is [Ar] 3d¹⁰ 4s².
- When Zn loses two electrons to form Zn²⁺, it loses the two 4s electrons, resulting in [Ar] 3d¹⁰.
- The 3d subshell is fully filled with 10 electrons.
- **Conclusion**: Zn²⁺ also obeys the octet rule.

### Step 3: Analyze Option C - SiCl4 (Silicon Tetrachloride)
- The structure of SiCl4 consists of one silicon atom bonded to four chlorine atoms.
- The Lewis structure can be represented as:
```
Cl
|
Cl-Si-Cl
|
Cl
```
- Silicon shares four electrons with four chlorine atoms, and each chlorine atom has three lone pairs, resulting in eight electrons around each chlorine.
- Silicon also has eight electrons around it due to the four bonds.
- **Conclusion**: SiCl4 obeys the octet rule.

### Step 4: Analyze Option D - CO (Carbon Monoxide)
- The structure of CO consists of one carbon atom triple-bonded to one oxygen atom.
- The Lewis structure can be represented as: C≡O.
- Carbon shares three electrons with oxygen, and oxygen has two lone pairs.
- Carbon has only six electrons around it (three from the triple bond) and oxygen has eight electrons (two from lone pairs and three from the triple bond).
- **Conclusion**: CO does not obey the octet rule as carbon only has six electrons.

### Final Answer
The compound that does not obey the octet rule is **Option D: CO (Carbon Monoxide)**.

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