Incorrect statement is :

Options

A. `AlF_(3) gt MgO gt MgF_(2)` : Lattice energy
B. `Li gt Na gt Al gt Mg` : Electron afinity
C. `SF_(6) gt PF_(5) gt SiF_(4)` : Lewis acidic character
D. `SiCl_(4) gt SiBr_(4) gt SiI_(4)` : Decreasing order of electronegativity of Si

Explanation

To determine the incorrect statement among the given options, we will analyze each option one by one based on the principles of chemistry, particularly focusing on lattice energy, electron affinity, Lewis acidity, and electronegativity.

### Step-by-Step Solution:

1. **Analyze Option A: AlF3 > MgO > MgF2 for lattice energy.**
- Lattice energy is the energy required to separate one mole of an ionic solid into gaseous ions.
- AlF3 has a higher lattice energy than both MgO and MgF2 due to the higher charge density of Al3+ compared to Mg2+ and the smaller size of F- compared to O2-.
- **Conclusion:** This statement is correct.

2. **Analyze Option B: Electron affinity order - Li > Na > Al > Mg.**
- Electron affinity generally increases across a period and decreases down a group.
- Lithium, being in the second period, has a higher electron affinity than sodium, which is in the third period.
- Sodium has a higher electron affinity than aluminum and magnesium, which are also in period 3 but in different groups.
- **Conclusion:** This statement is correct.

3. **Analyze Option C: SF6 > PF5 > SiF4 for Lewis acidic character.**
- Lewis acids are species that can accept a pair of electrons.
- SF6 has a full octet with six fluorine atoms surrounding sulfur, creating steric hindrance that prevents it from accepting additional electron pairs effectively.
- PF5, on the other hand, can accept electron pairs more readily than SF6 due to less steric hindrance.
- Therefore, the correct order of Lewis acidity is PF5 > SiF4 > SF6, making this statement incorrect.
- **Conclusion:** This statement is incorrect.

4. **Analyze Option D: SiCl4 > SiBr4 > SiI4 for electronegativity.**
- Electronegativity decreases down the group in the periodic table.
- Chlorine is more electronegative than bromine, which is more electronegative than iodine.
- Therefore, SiCl4 will have the highest electronegativity, followed by SiBr4, and then SiI4.
- **Conclusion:** This statement is correct.

### Final Answer:
The incorrect statement is **Option C: SF6 > PF5 > SiF4 for Lewis acidic character.**

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