Chemistry Question on Chemical bonding and molecular structure

Question

Which of the following substance has the highest melting point?

Answer 1

Solution

Melting points depend upon lattice energy, $NaCl$ and $KCl$ have unit charge on their ions while $MgO$ and $BaO$ have two units of charge, therefore lattice energies of $MgO$ and $BaO$ are expected to be larger than those of $NaCl$ and $KCl$ . Since, $Mg^{2+}$ is smaller than $Ba^{2+}$ , therefore, $MgO$ has the higher lattice energy and hence, has the higher melting point