Answer : Option A) The lattice energy increases as cations get smaller, as shown by LiF and KF.
Explanation : It is observed that lattice energy is mostly influenced by two main factors of an ionic solid which are;
i) The charge on the ions - As the charge of the ions increases, the lattice energy is observed to increase too.
and
ii) The radius, or size, of the ions - As the size of the ions increases, the lattice energy decreases with it.
So, here in this question the second reason is clearly observed. Hence, it is self-explained that the size of the cations are decreased in the ionic solids the lattice energy increases.