Melting point order is not correct is :-

Options

A. `NaF lt MgF_(2) lt AlF_(3)`
B. `NaCl gt MgCl_(2) gt AlCl_(3)`
C. `LiCl gt NaCl gt KCl gt RbCl`
D. `NaCl gt AgCl`

Explanation

To determine which order of melting points is incorrect among the given options, we need to analyze the factors that influence melting points in ionic compounds. The primary factors include ionic character, lattice energy, and the size of the ions involved.

### Step-by-Step Solution:

1. **Understanding Ionic Compounds**:
- Ionic compounds consist of cations and anions. The melting point of these compounds is influenced by the strength of the ionic bonds, which is affected by the size and charge of the ions.

2. **Analyzing the Given Options**:
- We need to evaluate the melting point orders presented in the options and identify the one that does not follow the expected trend based on ionic character and lattice energy.

3. **Option A**:
- The order is correct. For example, in aluminum fluoride (AlF3), the small fluoride ion (F-) is highly polarizable by the small Al3+ cation, leading to strong ionic interactions and a high melting point.

4. **Option B**:
- This option also appears correct. Larger anions lead to lower ionic character, and thus lower melting points. For example, Al3+ has a higher charge, leading to a decrease in ionic character compared to Na+.

5. **Option C**:
- This option needs careful consideration. All compounds listed are from the same group, and the melting point order should correlate with the ionic character. The smaller the cation, the higher the melting point due to stronger ionic character. Therefore, if the order presented does not follow this trend, it is incorrect.

6. **Option D**:
- This option is also correct. NaCl is indeed more ionic than AgCl due to Na being an alkali metal (more electropositive) compared to Ag, which is a transition metal. This results in NaCl having a higher melting point.

7. **Conclusion**:
- The incorrect order of melting points is found in **Option C**. This is because the expected trend based on ionic character and lattice energy is not followed.

### Final Answer:
The melting point order that is not correct is **Option C**.