Recall the dependence of lattice energy

Lattice energy is the energy released when oppositely charged gaseous ions come together to form an ionic solid.

From electrostatic attraction, it depends mainly on Coulomb’s law:

$U \propto \frac{q_1 q_2}{r}$

where:

• $q_1, q_2$ are the charges on the ions
• $r$ is the distance between the ions, which depends on ionic size

Interpret the formula

• If the charge on ions increases, attraction becomes stronger, so lattice energy increases.
• If the size of ions increases, the distance between ions increases, so attraction decreases and lattice energy decreases.

Thus, lattice energy depends on:

• charge of ions
• size of ions

Evaluate the options

• A: Charge on the ion only — Incorrect, because ionic size also matters.
• B: Size of the ion only — Incorrect, because ionic charge also matters.
• C: Packing of ions only — Incorrect, not the main dependence asked here.
• D: Charge on the ion and size of the ion — Correct.

Final answer

$\boxed{\text{D}}$