The molecule in which an atom is associated with more than 8 electrons is known as hypervalent molecule and less than 8 electrons is known as hypovalent molecule. All hypervalent molecules must have `ppi-dpi` bonding but the molecules having back bonding back boding need not to have always `ppi-dpi` bondin.
Q.Which of the molecule is not hypovalent but complete its octet:

Options

A. `AlI_(3)`
B. `AlCl_(3)`
C. `AlBr_(3)`
D. `AlF_(3)`

Explanation

To solve the question, we need to identify which of the given molecules is not hypovalent but still completes its octet. Let's analyze each option step by step.

### Step 1: Understand the definitions
- **Hypovalent molecule**: A molecule where the central atom has less than 8 electrons in its outermost shell.
- **Hypervalent molecule**: A molecule where the central atom has more than 8 electrons in its outermost shell.

### Step 2: List the given options
The options provided are:
1. AlI3
2. AlCl3
3. AlBr3
4. AlF3

### Step 3: Analyze each molecule
1. **AlI3**:
- Aluminium (Al) typically has 3 valence electrons and iodine (I) has 7. In AlI3, Al shares its 3 electrons with 3 I atoms, resulting in Al having less than 8 electrons (6 electrons). Therefore, AlI3 is hypovalent.

2. **AlCl3**:
- Similar to AlI3, in AlCl3, Al shares its 3 electrons with 3 Cl atoms. Al ends up with 6 electrons in its outer shell. Thus, AlCl3 is also hypovalent.

3. **AlBr3**:
- In AlBr3, Al again shares its 3 electrons with 3 Br atoms, resulting in Al having 6 electrons. Therefore, AlBr3 is hypovalent as well.

4. **AlF3**:
- In AlF3, Al shares its 3 electrons with 3 F atoms. However, fluorine is highly electronegative and each F atom has a complete octet (8 electrons). The ionic character of AlF3 means that Al can effectively complete its octet through ionic bonding. Therefore, AlF3 is not hypovalent and completes its octet.

### Step 4: Conclusion
Among the given options, the molecule that is not hypovalent but completes its octet is **AlF3**.

### Final Answer
**AlF3 (Option D)** is the molecule that is not hypovalent but completes its octet.

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