Can you compare the lattice enthalpies of the salts MgCl_2, and CaCl_2, and SrCl_2, and BaCl_2?

Neither $C s C {l}_{2}$ nor $S c C {l}_{2}$ exist..........
We could compare $M g C {l}_{2}$, and $C a C {l}_{2}$, and $S r C {l}_{2}$, and $B a C {l}_{2}$. Of these, $M g C {l}_{2}$ will have the highest lattice energy. Why?
Because $M {g}^{2 +}$ is the smallest ion, and thus the electrostatic force of attraction is GREATEST between the smaller metal cation and the chloride anion. And certainly, given the $\frac{1}{r} ^ 2$ electrostatic force, interaction between the cation and the anion will be here the most significant.