Incorrect statement is

Options

A. `MgO gt AlF_(3) gt MgF_(2):" Lattice energy"`
B. `Ni gt Na gt Mg:"Electron affinity"`
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"`

Answer

To determine the incorrect statement from the provided options, we will analyze each statement step by step.

### Step 1: Analyze Lattice Energy
- **Statement**: "MgO, AlF3, and MgF2 lattice energy."
- **Analysis**: Lattice energy is influenced by the charges of the ions and the distance between them. The formula for lattice energy is given by:
\[ U = \frac{k \cdot Q_1 \cdot Q_2}{R} \]
where \(Q_1\) and \(Q_2\) are the charges of the ions and \(R\) is the distance between them.
- For MgO: \(Q_1 = +2\), \(Q_2 = -2\) → \(U \propto 4\)
- For AlF3: \(Q_1 = +3\), \(Q_2 = -1\) → \(U \propto 3\)
- For MgF2: \(Q_1 = +2\), \(Q_2 = -1\) → \(U \propto 2\)

Thus, the lattice energy order should be MgO > AlF3 > MgF2, which is correct.

**Hint**: Lattice energy depends on the product of the charges of the ions.

### Step 2: Analyze Electron Affinity
- **Statement**: "Electron affinity of Li > Na > Mg."
- **Analysis**: Electron affinity is the energy change when an electron is added to a neutral atom.
- Lithium has a higher electron affinity than sodium because it is easier to add an electron to a smaller atom.
- Magnesium, with a filled outer shell (3s2), has a lower electron affinity than both Li and Na, making this order correct.

**Hint**: Electron affinity generally decreases down a group due to increasing atomic size.

### Step 3: Analyze Lewis Acidic Character
- **Statement**: "SF6 > PF5 > SiF4 in Lewis acidic character."
- **Analysis**: The Lewis acidic character is determined by the ability to accept electron pairs.
- SF6 is sterically hindered due to six fluorine atoms, making it a weak Lewis acid.
- PF5 can accept electron pairs but is less hindered than SF6.
- SiF4 is less acidic than PF5.

Therefore, the correct order should be PF5 > SiF4 > SF6, making the original statement incorrect.

**Hint**: Steric hindrance affects the Lewis acidic character of molecules.

### Step 4: Analyze Electronegativity Order
- **Statement**: "Decreasing order of electronegativity of SiCl4, SiBr4, SiI4."
- **Analysis**: Electronegativity decreases down the group in the periodic table.
- Thus, SiCl4 > SiBr4 > SiI4 is the correct order.

**Hint**: Electronegativity decreases with increasing atomic size in the same group.

### Conclusion
The incorrect statement is regarding the Lewis acidic character of SF6, PF5, and SiF4. The correct order should be PF5 > SiF4 > SF6, not SF6 > PF5 > SiF4.

### Final Answer
The incorrect statement is the one regarding the Lewis acidic character: "SF6 > PF5 > SiF4."