Question

Which of the following ionic compounds is likely to have the highest melting point?

• A. $NaCl$
• B. $AlN$
• C. $MgO$
• D. $K_{2}S$

Answer 1

Answer: (C)

$MgO$

According to Fajan's Rule, molecule low charge on cation, larger cation, and smaller anion have more of ionic character thereby having high lattice energy and hence have a higher melting point.

So, here $MgO$ with cationic-anionic charge as $2$ and anion $O^{2-}$ is smaller than $M{g}^{2+}$ have more of the ionic character and have high lattice energy and thus have a high melting point.