The lattice enthalpy of Na2O is –2600 kJ mol–1 while the lattice enthalpy of MgO is –3900 kJ mol–1. — Bonding Chemistry Question

The lattice enthalpy of Na₂O is –2600 kJ mol–1 while the lattice enthalpy of MgO is –3900 kJ mol–1. Which factors contribute to the larger magnitude of the lattice enthalpy of MgO?
I. Mg²⁺ has a larger charge than Na⁺.
II. Mg²⁺ is smaller than Na⁺.