In which of the following molecules does the central atom not follow the octet rule?

Options

A. `CH_(4)`
B. `overset(..)(P)H_(3)`
C. `BF_(3)`
D. `CO_(2)`

Explanation

To determine which of the given molecules has a central atom that does not follow the octet rule, we will analyze each molecule step by step.

### Step 1: Identify the Central Atom and Valence Electrons

1. **CH3 (Methane)**
- Central Atom: Carbon (C)
- Valence Electrons: 4
- Bonds: Carbon forms 4 single bonds with 4 hydrogen atoms.
- Total Electrons around Carbon: 4 (from C) + 4 (from 4 H) = 8
- **Conclusion**: Follows the octet rule.

2. **PH3 (Phosphine)**
- Central Atom: Phosphorus (P)
- Valence Electrons: 5
- Bonds: Phosphorus forms 3 single bonds with 3 hydrogen atoms.
- Total Electrons around Phosphorus: 5 (from P) + 3 (from 3 H) = 8
- **Conclusion**: Follows the octet rule.

3. **BF3 (Boron Trifluoride)**
- Central Atom: Boron (B)
- Valence Electrons: 3
- Bonds: Boron forms 3 single bonds with 3 fluorine atoms.
- Total Electrons around Boron: 3 (from B) + 3 (from 3 F) = 6
- **Conclusion**: Does not follow the octet rule (needs 2 more electrons to complete the octet).

4. **CO2 (Carbon Dioxide)**
- Central Atom: Carbon (C)
- Valence Electrons: 4
- Bonds: Carbon forms 2 double bonds with 2 oxygen atoms.
- Total Electrons around Carbon: 4 (from C) + 4 (from 2 O) = 8
- **Conclusion**: Follows the octet rule.

### Step 2: Summary of Findings
- **CH3**: Follows octet rule
- **PH3**: Follows octet rule
- **BF3**: Does not follow octet rule
- **CO2**: Follows octet rule

### Final Answer
The molecule in which the central atom does not follow the octet rule is **BF3**.

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