Question

Sort the given metal halides in increasing order of melting point.

• A. $NaI$
• B. $NaCl$
• C. $NaBr$
• D. $NaF$

Answer 1

Sodium halides are ionic in nature and melting point is greater for compounds which have higher ionic character.
According to Fajan's rules
$Covalentcharacter\propto sizeofanion$
$\propto \frac{1}{Sizeofcation}$
Here, the cation is fixed. So for comparing covalent character, we only compare size of $X^{-}$.
Order of ionic character is reverse of covalent character and thus order of melting point follows as
$NaI<NaBr<NaCl<NaF$.