In which of the following compounds does not
central atom obey the octet rule ?

Options

A. `XeF_(4)`
B. `XeOF_(2)`
C. `SCl_(2)`
D. `AlCl_(3)`

Explanation

To determine which of the given compounds does not have a central atom that obeys the octet rule, we will analyze each compound step by step.

### Step 1: Understanding the Octet Rule
The octet rule states that atoms tend to form compounds in ways that give them eight valence electrons, achieving a stable electron configuration similar to that of noble gases.

### Step 2: Analyze Each Compound

#### Compound A: XeF4 (Xenon Tetrafluoride)
1. **Valence Electrons in Xenon**: Xenon has 8 valence electrons.
2. **Bonding with Fluorine**: Each fluorine atom shares one electron with xenon.
3. **Total Electrons Around Xenon**: After forming 4 bonds with fluorine, xenon shares 4 electrons, resulting in 12 electrons around xenon (8 original + 4 shared).
4. **Conclusion**: Xenon does not obey the octet rule (expanded octet).

#### Compound B: XeOF2 (Xenon Oxyfluoride)
1. **Valence Electrons in Xenon**: Xenon has 8 valence electrons.
2. **Bonding with Fluorine and Oxygen**: Two fluorine atoms and one oxygen atom are bonded to xenon.
3. **Total Electrons Around Xenon**: After forming bonds, xenon shares 4 additional electrons (2 from F and 2 from O), resulting in 12 electrons around xenon.
4. **Conclusion**: Xenon does not obey the octet rule (expanded octet).

#### Compound C: SCl2 (Sulfur Dichloride)
1. **Valence Electrons in Sulfur**: Sulfur has 6 valence electrons.
2. **Bonding with Chlorine**: Two chlorine atoms share electrons with sulfur.
3. **Total Electrons Around Sulfur**: After forming 2 bonds, sulfur shares 2 electrons, resulting in 8 electrons around sulfur (6 original + 2 shared).
4. **Conclusion**: Sulfur obeys the octet rule.

#### Compound D: AlCl3 (Aluminum Chloride)
1. **Valence Electrons in Aluminum**: Aluminum has 3 valence electrons.
2. **Bonding with Chlorine**: Three chlorine atoms share electrons with aluminum.
3. **Total Electrons Around Aluminum**: After forming 3 bonds, aluminum shares 3 electrons, resulting in only 6 electrons around aluminum (3 original + 3 shared).
4. **Conclusion**: Aluminum does not obey the octet rule (incomplete octet).

### Final Conclusion
The compounds where the central atom does not obey the octet rule are:
- **XeF4** (expanded octet)
- **XeOF2** (expanded octet)
- **AlCl3** (incomplete octet)

Thus, the answer is **A, B, and D**.

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