. Identify the correct order of standard enthalpy of formation of sodium halides.

The lattice energy of an ionic compound is the energy required to separate one mole of the compound into its constituent ions in the gas phase.

 Lattice energy$\propto \frac{1}{\left(r_{+}+r_{-}\right)}$

The lattice energy is inversely proportional to the sum of the ionic radii $\left({\mathrm{r}}_{+}+{\mathrm{r}}_{-}\right)$ of the ions involved. When the size of the ions increases, the distance between them also increases, leading to a decrease in the attractive forces between the ions and a decrease in the lattice energy. Therefore, if the size of the ions increases, the lattice energy generally decreases.

So Order : $\mathrm{NaF} > \mathrm{NaCl} > \mathrm{NaBr} > \mathrm{NaI}$