Which of the following compounds has a positive enthalpy of solution? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Enthalpy of solution is positive (endothermic) when the energy required to break the crystal lattice (lattice energy) is greater than the hydration energy released upon dissolution. Step 2: In Lithium Fluoride (LiF), both the cation (Li^+) and anion (F^-) are exceptionally small, allowing them to pack extremely tightly together in the crystal lattice. Step 3: This tight packing leads to an extraordinarily high lattice energy that is not fully compensated by the hydration of the ions. Consequently, LiF is sparingly soluble in water with a positive enthalpy of solution, matching option (a).