Question

Based on lattice energy and other considerations which one of the following alkali metal chloride has the highest melting point?

• A. $KCl$
• B. $RbCl$
• C. $LiCl$
• D. $NaCl$

Answer 1

Answer: (D)

$NaCl$

The melting point of the alkali metals generally decreases down the group due to size mismatching (down the group size of the cation increases, size mismatching increases, hence lattice energy decreases). But the melting point of $LiCl$ is abnormally low than the other metal halides because of it's higher covalent character (Fajan's rule). So it is expected that $NaCl$ must have the highest melting point among all the alkali metal halides. So option D is correct.