The incorrect order of lattice energy is :

Options

A. `AlF_(3) gt MgF_(2)`
B. `Li_(3)N gt Li_(2)O`
C. `NaCl gt LiF`
D. `TiC gt ScN`

Explanation

To determine the incorrect order of lattice energy, we need to analyze the factors that influence lattice energy, which include the charges of the ions and the distance between them (ionic radii). Lattice energy is directly proportional to the product of the charges of the ions and inversely proportional to the distance between them.

### Step-by-Step Solution:

1. **Understanding Lattice Energy**:
Lattice energy is the energy required to separate one mole of an ionic solid into its gaseous ions. It can be represented by the formula:
\[ U \propto \frac{Q_1 \times Q_2}{r} \]
where \( Q_1 \) and \( Q_2 \) are the charges of the ions and \( r \) is the distance between the ions.

2. **Analyzing the Given Compounds**:
We will analyze the lattice energy of the following pairs:
- \( \text{LiF} \) vs \( \text{NaCl} \)
- \( \text{MgF}_2 \) vs \( \text{AlF}_3 \)
- \( \text{Li}_2\text{O} \) vs \( \text{Li}_3\text{N} \)
- \( \text{TiC} \) vs \( \text{ScN} \)

3. **Comparing Charges**:
- For \( \text{LiF} \): \( \text{Li}^+ \) (1+) and \( \text{F}^- \) (1−) → Charge product = 1
- For \( \text{NaCl} \): \( \text{Na}^+ \) (1+) and \( \text{Cl}^- \) (1−) → Charge product = 1
- For \( \text{MgF}_2 \): \( \text{Mg}^{2+} \) (2+) and \( 2\text{F}^- \) (1−) → Charge product = 2
- For \( \text{AlF}_3 \): \( \text{Al}^{3+} \) (3+) and \( 3\text{F}^- \) (1−) → Charge product = 3
- For \( \text{Li}_2\text{O} \): \( 2\text{Li}^+ \) (1+) and \( \text{O}^{2-} \) (2−) → Charge product = 2
- For \( \text{Li}_3\text{N} \): \( 3\text{Li}^+ \) (1+) and \( \text{N}^{3-} \) (3−) → Charge product = 3
- For \( \text{TiC} \): \( \text{Ti}^{4+} \) (4+) and \( \text{C}^{4-} \) (4−) → Charge product = 16
- For \( \text{ScN} \): \( \text{Sc}^{3+} \) (3+) and \( \text{N}^{3-} \) (3−) → Charge product = 9

4. **Considering Ionic Radii**:
- The smaller the ionic radii, the greater the lattice energy.
- \( \text{Li}^+ \) and \( \text{F}^- \) are smaller than \( \text{Na}^+ \) and \( \text{Cl}^- \), hence \( \text{LiF} \) has a higher lattice energy than \( \text{NaCl} \).

5. **Conclusion**:
Based on the analysis, the order of lattice energies can be summarized as follows:
- \( \text{AlF}_3 > \text{MgF}_2 \)
- \( \text{Li}_3\text{N} > \text{Li}_2\text{O} \)
- \( \text{LiF} > \text{NaCl} \)
- \( \text{TiC} > \text{ScN} \)

Therefore, the incorrect order of lattice energy is likely to be \( \text{NaCl} > \text{LiF} \), as \( \text{LiF} \) should have a higher lattice energy due to its smaller ionic sizes and higher charge product.