Final answer:
The lattice enthalpy of NaF is higher than that of NaCl due to the larger Na-F distance.
Step-by-step explanation:
The lattice enthalpy is a measure of the energy released when gaseous ions come together to form an ionic solid. It is influenced by both the charges of the ions and the distance between them.
In the case of NaCl and NaF, they have the same crystal structure as they both belong to the same group in the periodic table (alkali metals). However, the Na-F distance in NaF is larger than the Na-Cl distance in NaCl.
Since the lattice enthalpy depends on the product of the charges of the ions, a salt with a metal cation with a +2 charge and a nonmetal anion with a -2 charge will have a lattice energy four times greater than one with a metal cation with a +1 charge and a nonmetal anion with a -1 charge.
Therefore, the lattice enthalpy of NaF should be higher than that of NaCl.
Based on the information provided, the closest approximation of the lattice energy of NaF is 924 kJ/mol.