JEE Main 2023 — S Block Elements Question with Solution

Lattice energy is directly proportional to the charges of the ions and inversely proportional to the sum of their radii:

Lattice energy ∝ (Q₁Q₂) / (r₁ + r₂)

As we move down the group, the size of the halide ions increases, resulting in a decrease in lattice energy. This leads to a decrease in the exothermicity of the lattice energy release during the formation of sodium halides.

Thus, the correct order of standard enthalpy of formation of sodium halides, considering both lattice energy and electron affinity, is:

$$\mathrm{NaF}>\mathrm{NaCl}>\mathrm{NaBr}>\mathrm{NaI}$$