Question

Which of the following is not true for $NaCl$ and $MgO$?

• A. $NaCl$ has higher lattice energy than $MgO$.
• B. Magnesium oxide has a higher melting point than sodium chloride.
• C. Magnesium oxide is used to prevent and treat low levels of magnesium in the blood.
• D. The lattice energy associated with $MgO$ is higher as compared to $NaCl$.

Answer 1

The correct option is A $NaCl$ has higher lattice energy than $MgO$.

$L.E=\frac{k{q}_1{q}_2}{r}$
where, $k$=proportionality constant,
$q_1,q_2$ are the charges on the ions and
$r$ is the shortest distance between the centers of cations and anions.

Lattice energy is proportional to the charge on the ions and inversely proportional to the size of ions. Also, between charge and size, charge is the dominating factor.
The product of charges for NaCl is $|(+1)(-1)|$ and for MgO is $|(+2)(-2)|$.
Hence, lattice energy is more for $MgO$ than $NaCl$.