$\mathrm{AB}$ is an ionic solid. The ionic radii of ${\mathrm{A}}^{+}$ and ${\mathrm{B}}^{-}$ are respectively ${\mathrm{r}}_{\mathrm{c}}$ and ${\mathrm{r}}_{\mathrm{a}}$. Lattice energy of $\mathrm{AB}$ is proportional to

Lattice Energy. The force of attraction between oppositely charged particles is directly proportional to the product of the charges on the two objects (q₁ and q₂) and inversely proportional to the square of the distance between the objects (r₂).

$\mathrm{Latice} \mathrm{Energy} \mathrm{\alpha } \frac{{\mathrm{q}}_{\mathrm{c}}{\mathrm{q}}_{\mathrm{a}}}{{\mathrm{r}}_{\mathrm{c}}+{\mathrm{r}}_{\mathrm{a}}}$.